Components:
1) Sensory Senses changes in the
internal or external environment
2) Integrative Analyzes data, stores
data, decides which stimuli are important, and makes decisions regarding
appropriate behaviors.
3) Motor Responds to stimuli through
muscular contractions or glandular secretion.
2 Principle Divisions:
1) CNS Brain and Spinal Cord
Most impulses that stimulate muscles or glands originate in the CNS.
Connected to sensory receptors, muscles, and glands in the peripheral parts
of the body by the PNS.
2) PNS Cranial, spinal, peripheral
nerves
a. Afferent (sensory) neurons: impulses going to the CNS, Input.
b. Efferent (motor) neurons: impulses going away from the CNS, Output.
c. Association (interneurons) neurons: neither sensory nor motor.
Forms links between other neurons. Carries impulses from sensory
to motor. Integrative function.
d. Autonomic motor neurons (efferent) involuntary
Information to smooth muscle in the digestive, respiratory(bronchioles),
Cardiovascular(heart, blood vessels), and integumentary
systems(sweat glands).
Two divisions of PNS:
a. Somatic NS Sensory neurons that convey information from cutaneous
( pacinian corpuscles, mechanoreceptors, pain receptors, golgi
tendon organs) and special sense receptors(olfactory, retinal cells, auditory,
taste) to the CNS which direct impulses to skeletal muscle
(voluntary).
b. Autonomic NS Sensory receptors from the vicera to the CNS which direct
impulses to smooth muscle, cardiac muscle, and various
glands (involuntary).
Motor portion has 2 branches;
i. Sympathetic Fight or Flight Causes changes that prepare body for
immediate action.
1) Increases heart rate, breathing, dilates pupils
2) increases blood pressure, raises blood sugar.
ii. Parasympathetic Rest and Repose Causes changes that favors conservation
and storage of energy.
1) Slowing of heart rate, constriction of pupils
2) decreased BP, Increase insulin/facilitates storage of glucose.
Vicera receive instructions from both systems. Opposing functions
(usually).
Neuron Nerve cell with the ability to respond to stimuli
and convert the stimulus into a nerve impulse.
- small electrochemical current that controls nerve function.
- Three parts of Neuron:
1) Cell body (soma) nucleus surrounded by cytoplasm containing typical
organelles (lysosomes cellular digestion,
mitochondria cellular powerhouse/ATP production, gogi complexes
protein packaging/receptor production)
a. Additionally, neurons also contain Nissl bodies (protein synthesis)
and neurofibrils (support, cell shape) in their cytoplasm.
2) Dendrite (L.tree) input portion of neuron.
a. Relays info from the external environment to the cell body
b. Tree shaped array of dendrites converging on cell body.
c. Non-Myelinated.
3) Axon Thin, cylindrical projection (usually myelinated) that conducts
nerve impulses toward another neuron, muscle fiber, or gland cell.
a. Axons terminate at fine processes called axon terminals
b. Myelin Sheath (neurolemma) axons are surrounded by multilayered, phospholipid
containing, segmented coverings called myelin
sheaths (sheath of Schwann). Myelin sheaths serve to increase speed
of nerve impulse conduction and maintain health/integrity of the
fiber. (Saultatory conduction gap to gap)
c. Schwann Cells cells that create the myelin sheaths, closely associated
with axon.
d. Nodes of Ranvier gaps between Schwann cells
e. Multiple Sclerosis Disease process that creates hard scars (scleroses)
in the myelin sheaths. This sclerosis damages the neuron inside
the sheath so that they have impaired nerve conduction or no conduction
at all. Leads to muscle atrophy, coordination difficulties,
vision, hearing, etc problems depending what part of spinal cord or brain
MS is affecting.
Synapse The juction between two neurons or between a
neuron and its effector (muscle or gland). The tips of the axon terminals
swell into bulb shaped synaptic end bulbs (buttons, boutons).
Types of Synapses:
1) Axo-axonic
axon-axon synapse
2) Axo-somatic
axon-soma(cell body) synapse
3) Axo-dendritic
axon-dendrite synapse
Structural Class of Neurons-
1) Bipolar
Neuron has one dendrite and one axon (found in retinal, inner ear, olfactory
area of brain)
2) Unipolar
One process extending from cell body and are always sensory neurons.
3) Multipolar
Several dendrites, one axon. (brain, spinal cord)
Functional Classes of Neurons-
1) Sensory
(afferent) information to spinal cord
2) Motor (efferent)
information from spinal cord/brain to effectors
3) Interneurons
(association) all other neurons **90% of neurons in body are this type*.
Reflex Arc
Reflexes fast, predictable, automatic
responses to changes in the environment that help maintain normal physiological
activities.
1) Somatic
reflexes stimuli results in contration of skeletal muscles (knee jerk)
2) Visceral(autonomic)
reflexes responses of smooth muscle, cardiac muscle, and glands (heart
rate, respiration, digestion, urination, defecation)
Monosynaptic arc Sensory neuron sends
message directly to motor neuron
1) one synapse
2) knee jerk
Polysynaptic arc sensory neuron sends
message by way of an interneuron (association neuron) to several motor
neurons
1) stepping
on a tack withdrawal reflex (coordination of several muscles)
Receptor Organ: Receptor end of dendrite or specialized receptor cell in sensory organ.
Sensory Neuron: Dendrite, cell body, and axon of sensory neuron (unipolar). Transmits nerve impulse from receptor into spinal cord or brain.
Association Neuron Axon, dendrite,
cell body of
Neuron
within brain or spinal cord (serves as an integrative or processing cell)
Motor Neuron Axon, dendrite, cell
body of
.Transmits nerve impulse from brain and spinal cord to effector
organ.
Effector Organ responds to motor neuron impulse with an appropriate action (reflex, gland secretion, contraction).
End of lecture 1
Lecture 2:
CNS
1) Brain Largest and most complex
part of the nervous system
-estimated to have 100 billion neurons
A) 4 Parts
i. brainstem connects brain to spinal cord
1. Medulla oblongata
2. Pons
3. Midbrain
ii. diencephalon superior to brainstem
1. consists of thalamus and hypothalamus
2. located between the cerebral hemispheres
iii. cerebrum largest portion of mature brain
1. Occupies most of cranium
2. Has Right and Left hemispheres
iv. cerebellum inferior to cerebrum and posterior to brainstem
2)Spinal Cord
PNS
1) afferent and efferent nerves
2) 12 Pairs of cranial nerves arising
from brain
3) 31 pairs of spinal nerves arising
from spinal cord
Somatic fibers connect to skin and skeletal muscle
Autonomic fibers connect to viscera, blood vessels
Meninges of Brain and Spinal Cord Connective tissue coverings that encircle the spinal cord and brain.
3 Layers:
1) Dura mater
(tough mother) most superficial layer
a. Dense, tough, irregular connective tissue layer
b. Continues into vertebral canal as a stroing tube-like sheath that surrounds
the spinal cord.
c. Outer surface is called periosteal, inner surface is called meningeal.
d. Epidural Space space between dura and vertebral column, filled with
fat and connective tissue cushioning
e. Subdural Space deep to dura and superficial to 2nd meningeal layer
2) Arachnoid
mater (spidery mother) thin, spider-web like network of connective tissue
a. Continuous with the arachnoid of the spinal cord.
b. Subarachnoid Space deep to arachnoid and superpicial to 3rd meningeal
layer
3) Pia mater
(little mother) thinnest layer containing nerves and blood vessels.
a. Attached directly to surface of brain and spinal cord
b. Dentinculate ligaments thickenings of pia mater that suspend the spinal
cord in the middle of the dural sheath, protecting cord
from shock and displacement.
4) Meningitis
inflammation of the meninges (arachnoid and pia mater) due to bacterial
or viral infection.
a. Can result in mental status changes, loss of vision, hearing, progressing
to death without treatment
Cerebrum composed off an outer portion of grey matter
the cerebral cortex(neuronal) and an inner portion of while matter
(axonal).
Functions:
1) Controls
higher brain functions
2) Interprets
sensory impulses
3) Initiates
muscle movements
4) Stores
memory, reasoning, determines intelligence\
During Embryonic development the grey
matter develops faster then the while matter
1) Results
in infoldings of the brain
2) Folds are
called gyri (gyrus)
3) Deep grooves
between gyri are called sulci (sulcus)
4) Large grooves
that separate areas of the brain are called fissures
a. Longitudinal Fissure separates brain into R and L hemispheres.
i. The hemispheres are connected by a white matter bridge Corpus Callosum
ii. In 90% of the population, the Left hemisphere is dominant for language-related
activities of speech, writing, reading,
and complex intellectual functions (verbal, analytical, and computational
skills)
Lobes (bilateral)
1) Frontal
a. Most anterior portion of each cerebral hemisphere.
b. Bordered posteriorly by the central sulcus
c. Bordered inferiorly by lateral sulcus
d. Functions:
i. Concentration
ii. Planning
iii. Problem solving
iv. Primary motor area pre-central gyrus, just anterior to central sulcus
(homunculus map)
v. Motor speech area (Brocas area) in L hemisphere anterior to primary
motor cortex.
vi. Phineas Gage story
2) Parietal
a. Separated from frontal lobe by central sulcus
b. Post-central gyrus primary somatosensory area of cerebral cortex(touch,
temperature, pressure, pain) also homonculus map
c. Association area understanding speech, using words to express thoughts
and feelings (wernickes area L parietal lobe).
3) Temporal
a. Interprets sensory experiences especially auditory input.
b. Differentiates sounds as speech, music, noise
c. Responsible for hearing pitch and rhythm
4) Occipital
a. Combines visual images and other sensory experiences
b. Association relates present to past visual experiences and recognition
of what is seen
c. Sensory Primary visual area, detects shape, color, movement
d. black out with injury to occipital area of head
Diencephalon: 4 Parts
1) Thalamus
a. 3 cm long
b. relay station for sensory impulses that reach cerebral cortex from spinal
cord.
2) Hypothalamus
a. Thalamus Controls many body activity homeostasis
b. Links nervous systemm to endocrine system
c. Control Autonomic nervous system (smooth muscle, gland secretion, heart
rate, peristalsis, bladder fxn)
d. Associated with feelings of rage/aggression
e. Regulates body temperature
f. Hunger and thirst regulation
3) Epithalamus
(Pineal Gland)
a. secretes melatonin release governed by dark-light cycle, thought to
be involved with sleep cycles.
4) Ventricles (Third
Ventricle part of Diencephalon)
a. Fluid filled cavities within the brain.
i. Lateral ventricles located in the hemispheres of the cerebrum.
ii. 3rd Ventricle is a verticle slit anterior to, and at the midline of
the thalamus connecting the lateral ventricles and the 4th ventricle
iii. 4th Ventricle lies between the brain stem and the cerebellum
b. Filled with CSF (cerebrospinal fluid) clear, colorless fluid
i. Composed of glucose, proteins, lactate, electrolytes, and a few lymphocytes
ii. CSF circulates throught sub-arachnoid space, lateral ventricles, 3rd,
and 4th ventricles , as well as in the subarachnoid in spinal cord.
iii. Function of CSF:
a) Mechanical protection (brain is floating in CSF) from trauma
b) Chemical protection (blood brain barrier)
c) Circulates nutrients and waste products
Brain Stem
1) Pons (bridge connects spinal cord
with brain and parts of brain with each other)
a Rounded bulge on anterior of brainstem where it separates midbrain from
medulla oblongata
b. Relay nuclei in pons connect sensory and motor impulses from medulla(and
SC) to higher brain center
c. Important for arousal, alertness
d. Controls respiration along with medulla
2) Medulla Oblongata superior to
foramen magnum, inferior to Pons
b Contains all ascending and descending tracts that connect spinal cord
and various parts of the brain.
c. Pyramids on ventral side of medulla, contain large motor tracts passing
from the cerebral cortex to the spinal cord.
These fibers cross over as they enter the medulla (fibers from the Right
cortex cross to the left medulla and and supply
left sided musculature) = pyramidal decussation
d. Association Nuclei responsible for visceral reflexes
i. Heart rate
ii. Basic rhythm of breathing
iii. Regulates blood pressure by controling diameter (tone) of blood vessels
(and by heart rate)
Cerebellum - Inferior and posterior region of brain
1) Posterior
to medulla and pons, Inferior to occipital lobes
2) Function:
a. Maintains equilibrium, muscle tone, coordination
b. Integration sensory information received from receptors in muscles,
tendons, joints, and special sense organs (vestibulo-cochlear, visual)
End of lecture 2
Lecture 3:
Spinal Cord
1) Extends
from the medulla to the superior boarder of L2 in adults. Conducts nerve
impulses from brain to the periphery
2) Spinal
Nerves
a. Mixed nerves (motor, sensory, autonomic) that distribute to discrete
locations of the body. Originate from the joining of
anterior (motor) and posterior (sensory) roots from SC in the intervertebral
foramen. The posterior (dorsal) root has a
ganglion (dorsal root ganglion) which houses the cell bodies of sensory
neurons.
b. 31 pairs
i. 8 cranial (only 7 cervical vertebrae??)
ii. 12 thoracic
iii. 5 lumbar
iv. 5 sacral
v. 1 coccygeal
c. Rami: spinal nerve divides into several branches (rami) after.
i. Dorsal ramus serves deep muscles and skin of dorsal surface
of trunk
ii. Ventral ramus serves muscles and structures of upper and lower extremities
and lateral and ventral trunk.
iii. Rami communicantes components of the autonomic nervous system
d. Dermatomes: The skin of the entire body is supplied by spinal nerves
carrying somatic sensory information being carried
to spinal cord. All spinal nerves (except C1) supply branches to
the skin. The area of skin that provides sensory input to
each pair of spinal nerves is called a DERMATOME
e. Plexuses Ventral rami of spinal nerves (except T2-T12) form
networks (bilateral) by joining with other adjacent rami = plexus.
i. Cervical
ii. Brachial
iii. Lumbar
iv. Sacral
f. Intercostal Nerves (T2-T12) do not enter plexuses
i. Directly innervate the stuctures they supply.
3) Spinal Meninges
Same as cranial meninges
4) Conus medullaris
- Spinal cord tapers to a cone at about L2 level. There is
no spinal cord below L2, just nerves. Safe area
for lumbar puncture (spinal tap)
5) Cauda equina
horses tail roots of spinal nerves L! to S5,C1 that extend from
the conus medullaris and exit spinal canal at
their respective levels
6) Filum terminale
Extension of pia mater that extends inferiorly from conus and anchors
spinal cord to coccyx.
7) Regions
of Spinal Cord
a. Gray matter nerve cell bodies and unmyelinated (gray) axons of association
and motor neurons
i. Posterior horns
ii. central canal (contination of 4th ventricle extending the entire length
of SC)
iii. Lateral horns
iv. Anterior horns
v. Gray commissure
b. White matter bundles of myelinated axons of sensory and motor neurons.
i. Posterior funiculus (column) Main Sensory tracts
ii. Lateral funiculus motor, pain/temp, sensory
iii. Anterior funiculus motor, pain/temp, sensory
iv. White commisure anterior to gray commisure, axons from each side
of spinal cord cross over(decussate) at while commisure
c. Ascending Tracts = Sensory (tract = distinct bundle of nerve fibers
having a common origin or destination and carrying similar
information) Continuous with sensory areas in the brain
i. Spinothalamic tract (lateral and anterior) conveys information sensing
pain, temp, crude touch, deep pressure.
ii. Posterior column tracts or fasiculus gracilis, fasiculus cuneatus)
conveys sensory information:
a. Proprioception (muscle, tendon, joint movement and awareness)
b. Discriminative touch
c. Two-point discrimination
d. Pressure
e. vibration
d. Descending Tracts = Motor, continuous with sensory areas in the brain
i. Pyramidal tracts convey nerve impulses for precise, voluntary movemtents
of skeletal muscles
a. Lateral corticospinal
b. Anterior corticospinal
c. Corticobulbar
ii. Extrapyramidal tracts -convey nerve impulses for:
automatic movements
coordinating body movements with visual stimuli
maintainance of skeletal muscle tone/posture
maintainance of balance/equilibrium by regulating muscle tone in response
to head movements.
a. Rubrospinal
b. Tectospinal
c. Vestibulospinal
End of lecture 3
Beginning of Lecuture 4
Cranial Nerves Part of the PNS
1) 12 pair,
10 originate from the brainstem, all pass through foramina of the skull.
a. Some contain sensory nerves only, others are mixed(motor + sensory).
b. Motor fibers include somatic and autonomic efferent
2) Nerves
( type, function)
a. Olfactory (I) - Sensory
i. Smell
b. Optic (II) Sensory
i. Vision
c. Oculomotor (III) Motor
i. Eyelid, eye movement, pupillary constriction
d. Trochlear (IV) Motor
i. Eye movement
e. Trigeminal (V) Mixed
i. Chewing(motor), Sensation(touch , pain, temp) to face and forehead
f. Abducens (VI) Mixed
i. Lat. Movement of eye(Motor), proprioception of eye(sensory)
g. Facial (VII) Mixed
i. Mm of facial expression, saliva and tear excretion (motor), taste and
proprioception (sensory)
h. Vestbulocochlear (VIII)- Sensory
i. Vestibular Equilibrium, Cochlear hearing
i. Glossophyaryngeal (IX) Mixed
i. Saliva secretion, swallowing(motor), taste, BP regulation(sensory)
j. Vagus (X) Mixed
i. Visceral muscle movement, gland secretion(motor), Visceral sensation(sensory)
k. Accessory (XI) Motor
i. Swallowing, head mvts(SCM, traps motor), proprioception (sensory)
l. Hypoglossal (XII) Motor
i. Tongue movements(speech, swallowing)
Autonomic Nervous System Regulates activity of smooth
muscle, cardiac muscle, and glandular function.
Usually operates without
conscious control. Called autonomic because was originally thought
to function autonomously without the
interaction
of the CNS. Separated into two parts.
1) Autonomic Motor pathways:
a. Two neuron sequence. 1st neuron is called a preganglionic neuron.
Its cell body lies in the brain or spinal cord.
Its axon is myelinated a preganglionic fiber, which passes out of CNS
or spinal cord as a part of a cranial or spinal nerve.
The preganglionic fiber then separates from the nerve and synapses with
the post ganglionic neuron in a autonomic gangion.
The post ganglionic fiber (unmyelinated ) terminates in a visceral effector.
b. Ganglia Collection of cell bodies outside the CNS
c. Neurotransmitters:
i. All presynaptic fibers use Acetyl Choline.
ii. Postganglionic fibers of the Sympathetic division use Norepinephrine
(NE).
iii. Post ganglionic fibers of the Parasympathetic use Acetyl Choline (ACh).
d. Dual Innervation Organs tend to be supplied by both areas. Serve
opposing functions
2) Sympathetic division Excitation
a. Also known as the Thoracolumbar division Preganglionic neurons have
cell bodies in the lateral gray horns of T1-L2
b. Ganglia are close to CNS (sypathetic or paravertebral chain) and distant
from visceral effectors (divergence) -
short pregnglionic, long post ganglionic
c. Preganglionic fibers may synapse with 20 or more postganglionic fibers
that spread throught the body.
For this reason, sympathetic reponses are widespread reponses throughout
the body = fight of flight
3) Parasympathetic division inhibition
a. Craniosacral division preganglionic neurons have cell bodies in Cranial
nerves III, VIII, IX, X and in the lateral gray horns of S2-S4
b. Ganglia are terminal ganglia and are located at the end of the autonomic
motor pathway close to or within the wall of visceral organs
long preganglionic, short post ganglionic
c. Usually only synapse with 4-5 postganglionic fibers supplying the same
organ parasympathetic effects tend to be localized.
Cholinergic Neurons Ach = Acetylcholine
1) Neurotransmitter , released at synapse
2) All preganglionic neurons (both symp and para)
Adrenergic Neurons NE = Norepinephrine
1) Sympathetic postganglionic neurons
End of Lecture 4