Ner vou s Syst e m Cells of the Nervous System

Functions (CRIME) Neurons

1. Controlling muscles and glands.  Also called nerve cells
2. Receiving sensory input.  Receive stimuli, conduct action potentials,
3. Integrating information. transmit signals
4. Maintaining homeostasis.
5. Establishing and maintaining mental activity. Cell body – contains a single nucleus; source of
information for gene expression n
Divisions of the Nervous System
I. Central Nervous System Dendrites – extensions of the cell body; receive
 Brain and spinal cord information from other neurons; transmit the info
toward the neuron cell body
II. Peripheral Nervous System
 Nerves and ganglia Axon – single long cell process; conduct action
a. Sensory Division – afferent (toward) potentials from one part of the brain or spinal cord to
division; conducts action potentials from another part
sensory receptors to the CNS  Axon of sensory neurons – conduct action potentials
towards the CNS
 Sensory neurons – neurons that
transmit action potentials from the  Axon of motor neurons – conduct action potentials
periphery to the CNS away from the CNS

i. Somatic Sensory Fibers – carry info from Axon hillock – where the axon leaves the neuron cell
stimuli coming from the skin, skeletal, body
muscles, joints
ii. Visceral Sensory Fibers – transmits Nissl bodies – rough ER found in the cell body of a
impulses coming from the visceral neuron
organs
Schwann cells – form a myelin sheath (increases speed
of impulse transmission)
b. Motor Division – efferent (away) division;
conducts action potentials from the CNS
to effector organs Collateral axons – branches of axons
 Motor neurons – neurons that Types of Neurons
transmit action potentials from the
1. Multipolar neurons – many dendrites + a single
CNS toward the periphery axon
i. Somatic Motor Nervous System / 2. Bipolar neurons – two processes: 1 dendrite + 1
Voluntary – transmits action potentials axon
form the CNS to the skeletal muscles
3. Pseudo-unipolar neurons – single process that
ii. Autonomic Motor Nervous System / divides into 2 processes: extends to the
Involuntary – transmits action periphery + extends to the CNS
potentials from the CNS to cardiac,
smooth muscles and glands Neuroglia
1. Sympathetic – figth-or- flight  Non-neuronal cells of the CNS + PNS
system
 More numerous than neurons
2. Parasympathetic– resting &
digesting system  Retain the ability to divide

iii. Enteric Nervous System – unique 1. Astrocytes – major supporting cells in the CNS;
subdivision; both sensory and motor stimulate/inhibit the signaling activity of nearby
neurons contained within the neurons; help limit damage to neural tissue
digestive tract Blood brain barrier – protects neurons from
toxic substances in the blood; allows
exchange of waster products + nutrients

2. Ependymal cells – produce cerebrospinal fluid;

help move the cerebrospinal fluid through the CNS

3. Microglia – act as immune cells of the CNS’

protect the brain by removing bacteria and cell
debris
4 – 5. Oligodendrocytes (CNS) and Schwann
cells (PNS) – provide an insulating material that 1. Reception – stimuli received by visual receptors in
surrounds axons the eye
2. Transmission – sensory neurons transmit info to
Neural Signaling CNS
 Communication among neurons
 3. Integration – info given is interpreted and an Electrical Signals and Neural Pathways
appropriate response is determined Resting Membrane Potential
4. Transmission – the CNS transmits info to Polarized cell membrane – uneven distribution of
motor neurons charge

5. Actual response – muscle/glands receive info Resting membrane potential – uneven charge
and instruction from motor neurons distribution in an unstimulated/resting cell; polarized
 Higher concentration of K+ inside CM
Myelin Sheaths  Higher concentration of Na+ outside CM
 Highly specialized insulating layer of cells  Greater permeability of CM to K+ than to Na+

Unmyelinated axons – action potentials are conducted Leak channels – always open
slowly bcos in travels along the entire axon
Gated channels – closed until opened by specific signals
Myelinating axons – action potentials are conducted
rapidly by salutatory conduction Chemically gated channels – opened by
neurotransmitters
Nodes of Ranvier – gaps in the myelin sheath; where
ion movement can occur Voltage gated channels – opened by a change in
membrane potential
Organization of Nervous Tissue
Gray Matter – groups of neuron cell bodies + their Sodium potassium pump – required to maintain the
dendrites; very little myelin greater concentration of Na+ outside the CM and K+
 In the CNS; inside
 Cortex – GM on the surface of the brain
 Nuclei – GM located deeper within the Action Potentials
brain Excitable cells – RMP changes in response to stimuli
 In the PNS; that activate gated ion channels
 Ganglion – a cluster of neuron cell
bodies Local current – Na+ diffuses quickly into cell

White Matter – bundles of parallel axons + myelin Depolarization – a change that causes the inside of the
sheaths CM to become positive
 In the CNS
Local potential – result of depolarization
Nerve tracts – conduction pathways;
propagate action potentials from one
area of the CNS to another Threshold value – attainable local potential (critical pt.)
 In the PNS; Action potential – constitution of depolarization and
Nerves – bundles of axons + connective repolarization
tissue sheaths
Hyperpolarization – the charge on the CM briefly
becomes more negative than the RMP

All-or-none fashion – threshold is reached = action

potential occurs; if the threshold is not reached = action
potential doesn’t occur

Continuous conduction – the action potential is

conducted along the entire axon CM

Saltatory conduction – action potentials jump from one

node of Ranbier to the next

The Synapse
Synapse – a junction where the axon of one neuron
interacts with another

Presynaptic terminal – end of the axon

Postsynaptic membrane – membrane of the dendrite or

effector cell

Synaptic cleft – space separating the presynaptic &

postsynaptic membrane
Neurotransmitters – chemical messengers

Synaptic vesicles – where neurotransmitters are stored

Hyperpolarized – the inside of the postsynaptic cell

tends to become more negative

Substance Effect Clinical Example

Acetylcholine Excitatory or Alzheimer disease
inhibitory
Norepinephrine Excitatory Cocaine and
amphetamines
Serotonin Generally Mood, anxiety, and
inhibitory sleep induction
Dopamine Excitatory or Parkinson disease
inhibitory
Gamma- Inhibitory Treatment of
aminobutyric epilepsy
acid
Glycine Inhibitory Poison strychnine
Endorphins Inhibitory Opiates morphine
and heroin

Reflexes
Reflex – an involuntary reaction in response to a
stimulus applied to the periphery and transmitted to
the CNS

Reflex arc – neuronal pathway by which a reflex occurs

 Sensory receptor
 Sensory neuron
 Interneurons
 Motor neuron
 Effector organ (muscle or glands)

Neuronal Pathways
Converging pathway – two or more neurons synapse
with the same neuron

Diverging pathway – the axon from one neuron

divides and synapses with more than one other
neuron

Summation – allows integration of multiple sub

threshold local potentials; brings the membrane
potential to threshold and trigger an action potential

Spatial summation – local potentials originate from

diff. locations on the postsynaptic neuron

Temporal summation – local potentials overlap in time

Spinal co r d 1. Dorsal (posterior)

2. Ventral (anterior)
 Extends from the foramen magnum to the 2 nd
3. Lateral Columns
lumbar vertebra
a. Ascending tracts – conduct action
 Provides a two-way conduction pathway to and potentials toward the brain
from the brain b. Descending tracts – conduct action
potentials away from the brain
Cauda equina – inferior end of the SC; spinal nerves
exiting there resemble a horse’s tail Gray Matter of the SC (shaped like the letter H)
1. Posterior horns
2 Main Functions 2. Anterior horns
1. Transmits info to and from the brain. 3. Small lateral horns
2. Controls many reflex activities of the body.
Central canal – fluid filled space in the center of the cord
White Matter of the SC
 Spinothalamic tract – transmits pain, light touch, and
Ventral root – formed by ventral rootlets; deep pressure
Dorsal root – formed by dorsal rootlets Dorsal column – transmission of proprioception, touch,
deep pressure, vibration
Dorsal root ganglion – ganglion in a dorsal root
Spinocerebellar tracts – proprioception to cerebellum
Relfex Action
 Predictable, automatic response to a specific Descending Tracts
stimulus
Pathways that carry impulses from the brain to the
periphery
1. Reception of the stimulus.
2. Transmission of info to the CNS. Lateral corticospinal – muscle tone and skilled
3. Integration (interpretation and determination movements (hand)
of an appropriate response).
4. Transmission of info from the CNS to a Anterior corticospinal – muscle tone and movement of
muscle. trunk muscles
5. Actual response.
Rubrospinal – movement coordination
Spinal Cord Reflexes Reticulospinal – posture adjustment
Knee-Jerk Reflex
Stretch flex – simplest reflex; muscles contract in Vestibulospinal – posture & balance
response to a stretching force applied to them Tectospinal – movement in response to visual reflexes

Knee-jerk reflex – patellar reflex; used to determine if Cranial Nerves

the higher CNS centers that normally influence this  Transmit info to the brain form the sensory
reflex are functional receptors
 12 pairs
Withdrawal Reflex
Withdrawal Reflex – flexor reflex; to remove a limb Name Specific Function
from a painful stimulus I. Olfactory S S: smell
II. Optic S S: vision
Ascending Tracts M: 4-6 extrinsic eye
 Pathways that carry impulses form III. Oculomotor M muscles; P: constricts
the periphery to various parts of pupils
the brain IV. Trochlear M M: 1 extrinsic eye muscle
S: face + teeth; M: muscles
V. Trigeminal B
of mastification
VI. Abducens M M: 1 extrinsic eye muscle
S: taste; M: facial muscles;
VII. Facial B
P: salivary + tear glands
Acoustic /
VIII. Vestibulococh- S S: hearing + balance
lear
S: taste + touch to back of
Glossopharyng
IX. B tongue; M: pharyngeal
-eal
muscles; P: salivary glands
S: pharynx, larynx, viscera;
M: palate, pharynx, larynx;
X. Vagus B
P: viscera of thorax +
abdomen
M: 2 neck + upper back
XI. Accessory M
muscles
XII. Hypoglossal M M: tongue muscles

Spinal Nerves
 Arise along the spinal cord; contains mixed
nerves
 31 pairs
 8 Cervical
 12 Thoracic
 5 Lumbar
 5 Sacral Mixed nerves – contains both sensory and somatic motor
 1 Coccygeal neurons
Plexuses – where nerves come together and then Autonomic Nervous System
separate
 Preganglionic neuron
 Cervical plexus
 Postganglionic neuron
 Brachial plexus
 Maintain internal homeostasis
 Lumbosacral plexus
Autonomic ganglia – where preganglionic neurons
Cervical Plexus synapse with postganglionic neurons
Originates from spinal nerves C1 to C4
I. Sympathetic ANS
Phrenic nerve – most important branc of the CP;  ‘Fight-or-flight’
innervates the diaphragm (responsible for our ability
to breathe)  Prepares the body for action
 Most active during stressful situations
Brachial Plexus  Norepinephrine (main neurotransmitter)
 Originates from the spinal nerves C5 to T1
II. Parasympathetic ANS
1. Axillary nerve – innervates 2 shoulder  Activities result in conserving and restoring
muscles energy
+ the skin over part of it  Helps return the body to resting conditions
 Active during periods of calm and rest
2. Median nerve – innervates the anterior  PS fibers are in the vagus nerve
forearm and intrinsic muscles
Autonomic Neurotransmitters
3. Radial nerve – innervates all the muscles in Acetylcholine – neurotransmitters of the
the posterior arm and forearm + skin over the parasympathetic division
posterior surface of the arm, forearm, hand
Norepinephrine – postganglionic neurons of the
4. Musculocutaneous nerve – innervates the sympathetic division
anterior muscles of the arm + skin over the
radial surface of the forearm Functions of the Autonomic Nervous System
Sympathetic Division
5. Ulnar nerve – innervates most of the anterior  Prepares a person for action by increasing HR,
forearm muscles and some of the intrinsic BP, respiration, release of glucose
hand muscles + skin over the radial side of the
hand Parasympathetic Division
 Involuntary activities at rest: digestion of food,
Lumbosacral Plexus defecation, urination
Originates from spinal nerves L1 to S4
Enteric Nervous System
1. Obturator nerve – innervates the muscles of  Consists of plexus within the wall of the
the medial thigh + skin over it digestive tract

2. Femoral nerve – innervates the anterior thigh 1. Sensory neurons – connect the digestive tract to
muscles + skin over it & medial side of the leg the CNS
2. Sympathetic & parasympathetic neurons –
3. Tibial nerve – innervates the posterior thigh connect the CNS to the digestive tract
muscles, the anterior & posterior leg muscles, 3. Enteric neurons – located entirely within enteric
most of the intrinsic foot muscles + skin over plexus
the sole of the foot
Capable of monitoring and controlling the
digestive tract independently of the CNS
4. Common fibular nerve – innervates the
muscles of the lateral thigh & leg, some
intrinsic foot muscles + skin over the anterior
& lateral leg, dorsal surface of the foot

Sciatic nerve – CT sheath that bounds the tibial and

common fibular nerve
 Connects the spinal cord to the remainder of the
Brain brain
 Soft, wrinkled mass of tissue that is highly  Controls the heart rate, blood pressure, and
complex and adaptive; 3 pounds breathing
 25 billion neurons  Damage can cause death
 Requires a continuous supply of oxygen and
glucose 1. Medulla Oblongata
 Most inferior portion of the brainstem
I. Brainstem
 Important reflex actions like vomiting, sneezing,
 coughing, swallowing 2. Epithalamus
 Gray matter consists of various nuclei that serve  Smallest area superior + posterior to the
as vital centers thalamus
Cardiac centers – control HR  Consists of few small nuclei (emotional and
Vasomotor centers – regulates BP bu visceral response to odors) + pineal gland
controlling blood vessel diameter
Respiratory centers – initiates and Pineal gland – an endocrine gland that may influence
regulates breathing the onset of puberty; role in controlling some long term
Pyramids – two prominent enalargements cycles

2. Pons (bridge) 3. Hypothalamus

 Relay information bet. the cerebrum and the  Most inferior part
cerebellum  Consists of several small nuclei; maintaining
 Resembles an arched footbridge homeostasis
 Regulates respiration, swallowing, sleep  Control of body temp., hunger, and thirst
 Sensations such as sexual pleasure, rage, fear,
3. Midbrain and relaxation
 Smallest region of the brainstem
 4 mounds called the colliculi Important Homeostatic Mechanisms
 2 inferior; major relay centers for the 1. Control center of the ANS.
auditory nerve pathways in the CNS 2. The link bet. the nervous and endocrine
 2 superior; visual reflexes and receive systems.
touch and auditory input 3. Helps maintain fluid balance.
Anti-diuretic hormone (ADH) - regulates
4. Reticular Formation water excretion by the kidneys
 A group of nuclei scattered throughout the 4. Regulates body temperature.
brainstem 5. Regulates food intake (appetite and satiety
 Regulating cyclical motor functions; respiration, centers).
walking, chewing 6. Regulates sleep-wake cycles.
 Damage can result in coma 7. Influences sexual behavior and emotional
aspects of sensory input.
Reticular activating system – plays an
important role in arousing and maintaining Infundibulum – controlling the secretion of hormones
consciousness from the pituitary gland

II. Diencephalon Mammillary bodies – involved in emotional responses

to odors and in memory
 Part bet. the brainstem and the cerebrum
III. Cerebellum
1. Thalamus
 Second largest part of the brain; 2 hemispheres
 Largest part of the diencephalon
 Responsible for coordination of movements
 Major relay center for all sensory info (except
smell) to the cerebrum; plays a gating rol Comparator – a sensing device that compares data
from two sources
 Influences mood and registers an
uncomfortable perception of pain Proprioceptive neurons – innervate joints, tendons,
muscles; provide info about the position of body
Interthalamic adhesion – connects the two large, parts
lateral parts of the thalamus
1. Helps in smooth and coordinated body
movements (comparator function).
2. Maintains muscle tone posture.
3. Maintain balance and equilibrium
4. Important in learning motor skills.

IV. Cerebrum
 Largest and most prominent part of the brain

1. Sensory Function – receives info from sensory

receptors and interprets it
2. Motor Function – responsible for all voluntary
movement and some involuntary ones
3. Association Function – responsible for all of the
intellectual activities of brain
4 Lobes motivation, aggression, mood, olfactory reception
1. Frontal Lobe Primary motor area: consciously move our skeletal
 Control of voluntary motor functions, muscles
 Broca’s area – speech center Right and Left Hemispheres
Prefrontal area – reposible for executive Right hemisphere – three dimensional or spatial
functions perception, musical ability
2. Parietal Lobe Left Hemisphere – analytical hemisphere; mathematics
General Sensory Area – receives info from the and speech
sensory receptors in the skin and joints
Wernicke’s area – sensory speech area Memory
Working memory – stores info required for the
3. Occipital Lobe immediate performance of a task; 7 digit phone no.
 Receiving and perceiving visual input
Primary visual area – receives visual info Short-term memory – last longer; can be retained for a
Visual association area – portion where visual info few mins. to a few days
is integrated
Long-term memory – stored for only a few minutes or
4. Temporal Lobe become permanent by consolidation
Primary auditory area – center for reception of
auditory messages Consolidation – a gradual process involving the
formation of new and stronger synaptic connections
Auditory association area – where auditory
messages are integrated
Declarative memory – explicit memory; retains facts and
Psychic cortex – abstract thoughts related emotional undertones
and judgments
Procedural memory – reflexive memory; development
Gyri – folds and convolutions; increase the surface of motor skills
area of the cortex and intervening grooves (sulci)
Memory engrams – memory traces; long-term retention
Sulci – shallow grooves of a thought/idea
Fissures – deep groves
Limbic System
Longitudinal fissure – divides the cerebrum into left  A group of interconnected nuclei involved in
and right hemispheres memory and regulation of emotion

Cerebral cortex – outermost layer of the cerebrum; Hippocampus – formation and retrieval of memories
consists of gray matter
Amygdala – filter sensory info and evaluates it in terms
of emotional needs
Corpus callosum – connects the right and left
hemispheres
Meninges, Ventricles, and Cerebrospinal Fluid
Central sulcus – separates the frontal and parietal Meninges
lobes  Surround and protect the brain and spinal cord

Lateral fissure – separates the temporal love from the 1. Dura mater – most superficial and thickest
rest meninges
Epidural space – bet. the dura mater & the
Insula – fifth lobe; deep within the fissure vertebrae
Epidural anesthesia – clinically important as
Basal Nuclei the injection site of spinal nerves; given
 Group of functionally related nuclei to women during childbirth

Corpus striatum – located deep within the cerebrum 2. Arachnoid mater – thin, wispy, 2nd meningeal
membrane
Substantia nigra – darkly pigmented cells in the Subdural space – space bet. the dura mater
midbrain and the arachnoid mater; contains small
amt. of serous fluid
Spinal block – to inject anesthetic into the
area
Spinal tap – to take a sample of CSF

3. Pia mater – 3rd meningeal membrane; very

tightly bound to the surface of the brain and
spinal cord; filled with CSF and contains blood
vessels
Ventricles
Subarachnoid space – bet. the arachnoid and pia matter
Aph absent/defective
asia speech/language Brain Waves and Consciousness
comprehension
 Fluid filled cavities Electroencephalogram (EEG) -

Lateral ventricle – relatively large cavity in each Brain waves – wave like patterns
cerebral hemisphere
Alpha waves – awake but in a quiet, resting state with
Third ventricle – a smaller, midline cavity eyes close

Fourth ventricle – located at the base of the cerebellum Beta waves – occur during intense mental activity

Cerebral aqueduct – a narrow canal that connects the Delta waves – occur during deep sleep in infants and in
3rd and 4th ventricle patients

Cerebrospinal fluid Theta waves – observed in children; also in adults who

 Provides a protective cushion around the CNS are frustrated or have brain disorders

Choroid plexus – produces CSF; specialized Effects of Aging on the Nervous System
structures made of ependymal cells  Motor functions decline
 Mental functions (memory) decline
Arachnoid villi – structures that project from the
arachnoid layer; where blood is reabsorbed

Hydrocephalus – accumulation of CSF in the

ventricles

Motor Functions
Involuntary movements – occur without a conscious
thought

Voluntary movements – consciously activated to

achieve a specific goal; walking, typing

Upper motor neurons – have cell bodies in the

cerebral cortex

Lower motor neurons – have cell bodies in the

anterior horn

Motor Areas of the Cerebral Cortex

Primary motor cortex – control voluntary movements
of skeletal muscles

Premotor area – where motor functions are organized

before they are actually initiated in the primary motor
cortex

Pre-frontal area – where planning and initiating

movements occur

Other Brain Functions

Communication bet. the Right & Left
Hemispheres Commissures – connection bet. the
two hemispheres

Corpus callosum – largest commissure

Speech
Sensory speech area – Wernicke area; a portion of the
parietal lobe

Motor speech area – Broca area; inferior portion of the

frontal lobe