V. Nervous System

Functions of the Nervous System

1. Sensory Input
2. Integration
3. Homeostasis
4. Mental Activity
5. Controls of Muscles and Glands

Components of the Nervous System

1. Brain
2. Spinal Cord
3. Nerves
4. Sensory Receptors

Subdivision of the Nervous System

1. Central Nervous System (CNS)
2. Peripheral Nervous System (PNS)

Withdrawal Reflex

withdraw certain part of the body from the pain stimulus;
subconscious control

Process:
Pain Receptors -
[received] Nociceptors -
Sensory Neuron [deliver signal] -
CNS [Brain and Spinal Cord] -
Motor Neuron [carry response]-
Target Organ - [cause contraction]

Central Nervous System (CNS)

· Encased in bone
· Brain and Spinal Cord

Peripheral Nervous System (PNS)

· Not encased in bone
· Contain both motor and sensory neurons

Major Level of Central Nervous System

1. Spinal Cord Level
2. Lower Brain Subcortical Level
3. High Brain Cortical Level

Spinal Cord

[1] Walking movement;

[2] Reflexes that withdraw portion of the body from painful object;

[3] Reflexes that stiff the legs to support the body against gravity;

[4] Reflexes that control local blood vessel, GI movement and urinary excretion; and

[5] Concerned primarily with automatic, instantaneous motor response of the body to sensory stimuli

Lower Brain Subcortical Level

· Medulla Oblongata, Mesencephalon, Hypothalamus, Thalamus, Cerebellum and Basal Ganglia

Lower Brain Subcortical Level responsible for

[1] Subconscious control of arterial pressure and respiration (medulla and pons)

[2] Feeding reflexes, salivation and licking of the lips (medulla, pons, mesencephalon, amygdala and hypothalamus)

[3] Emotional pattern such as anger, sexual response, reaction to pain, pleasure

High Brain Cortical Level

Cerebellum, Basal ganglia, Hypothalamus and Cerebral Cortex

High Brain Cortical Level Function

· Store memory
· Function in association with the lower center of the nervous system
· Converts imprecise function of the lower brain center to determination and precise operation
· Essential for most of out thought process (but cannot function alone)

Brain three developmental divisions:

Forebrain, Midbrain and Hindbrain

Forebrain

Cerebrum [Telencephalon]
Thalamus [Diencephalon], Hypothalamus [Diencephalon]

Midbrain

Region between the hindbrain and the forebrain; it is important for hearing and sight.
: comes from Mesencephalon

Hindbrain

Medulla Oblongata, Pons and Cerebellum

Brainstem

Medulla Oblongata, Pons and Midbrain

Cerebrum

· 7/8 of the brain's weight

: Surface layer of gray matter (cerebral cortex) is greatly expanded by convolutions or gyri

Functions of Cerebrum

· Responsible for discriminatory identification and integration
· Memory
· Reasoning
· Use of language
· Emotional behavior
· Initiation of movement

Cerebrum Four Major Lobes

Frontal, Parietal, Temporal and Occipital

Frontal Lobe

Voluntary motor function, motivation, aggression, sense of smell, mood

Parietal Lobe

Reception and evaluation of sensory information except smell, hearing, and vision

Occipital Lobe

Reception and integration of visual input

Temporal Lobe

Reception and evaluation for smell and hearing; memory, abstract thought, judgment

Thalamus

: relay center of sensory impulse
Paired mass of gray matter situated below corpus callosum

A. Subthalamus
B. Epithalamus

Function of Thalamus

[1] Relay center for sensory impulses

[2] Responsible for crude awareness of sensation

[3] Processes and relays coordinating motor impulses from the basal ganglia and cerebellum to the cerebral motor cortex

[4] Relay and integration center for emotional behavior

Subthalamus

· Involved in controlling motor function

Epithalamus

· Connects the limbic system to other parts of the brain

Pineal Gland

· Hypothetically causes sleepiness [melatonin]
· Helps regulate biological clock
· May play a role in onset of puberty

GnRH is produced by _____________________which targets the ___________________ to release FSH and LH [important in Males and Females Reproductive Activity]

Hypothalamus; Anterior Pituitary Gland

Follicle Stimulating Hormone (FSH)

a hormone secreted by the anterior pituitary gland that promotes the formation of ova or sperm.

Luteinizing Hormone (LH)

causes ovulation; stimulates the secretion of progesterone by the corpus luteum;

causes the secretion of testosterone in the testes

Hypothalamus

[1] Regulation of body temperature,
[2] feeding activities,
[3] concentration and volume of ECF,
[4] ANS responses,
[5] endocrine functions

Regulation of Body Temperature,

Decrease in Temperature
| detected by
Thermoreceptor
| send the information
Sensory Neuron
| send to
Hypothalamus
| sends motor response to
Motor Neuron
| send signals to

A.
Arrector Pili Muscle [cause contraction]
| causes goosebumps
Increasing Body Temperature

B.
Skeletal Muscle
Causes contraction [shivering];
Increases Body Temperature

Concentration and Volume of ECF
Stimulus A

Stimulus: Increase Osmolarity in Blood
| ECF volume is low [low blood volume]; hypothalamus responds
Hypothalamus stimulates the production of ADH [Antidiuretic Hormone] - diuresis [pag-ihi]; prevents pag-ihi
| sends to
Posterior Pituitary Gland - release the ADH
| ADH moves into the blood [circulation] towards the Kidney
Kidney [Target Organ] - causes reabsorption of water
|
Renal Veins [filtered blood];
Inside volume increases; increasing blood volumes increase hydrostatic pressure and decrease osmotic pressure [gives negative feedback on the stimulus]

Pathway: Renal Artery - Afferent - Glomerulus - Efferent - Renal Veins

Concentration and Volume of ECF
Stimulus B

Stimulus: Thirst Reflex
Urge to drink water; increase the ECF volume
[gives negative feedback on the stimulus]

ANS Response

Hypothalamus an choose between sympathetic and parasympathetic

Endocrine Function

Has Neuroendocrine Cells; it can produce hormone ADH and Oxytocin that is secreted by the Posterior Pituitary Gland

Hypothalamus

· Receives input from viscera, taste receptors, limbic system, nipples, external genitalia, prefrontal cortex, efferent fibers to brainstem, spinal cord, through infundibulum to posterior pituitary, and to cranial nerves controlling swallowing and shivering

Cerebellum

· Integration center for promoting smooth, coordinated, voluntary movements

· Receives input from proprioceptors and receptor for touch, vision, and hearing as well as from motor cortex

· Sends inhibitory signals to monitor cortex that prevent inappropriate movements

· Involved in control of locomotion, posture, balance and eye movements

· Fine motor coordination leading to smooth, flowing movements, works with cerebrum to plan, practice, learn complex movements

Nystagmus

a term to describe uncontrollable movements of the eyes that may be:

o Side to Side (horizontal nystagmus)
o Up and Down (vertical nystagmus)
o Rotary (rotary or torsional nystagmus)

Pons

· Lies anterior to cerebellum between midbrain and medulla

: Bridge-like structure consisting almost entirely of white matter, linking various parts of the brain

: Sleep center and respiratory center - coordinates with center in medulla

Medulla Oblongata

· Continuous with spinal cord through foramen magnum
· Ventrally are pyramids (corticospinal tracts)

Medulla Oblangata Functions:

· Contains pathways for discriminatory touch and kinesthesia

· Contains centers for regulating:
1. Cardio-Vascular Function
2. Maintaining and controlling breathing
3. Coordinating swallowing
4. Vomiting
5. Coughing
6. Sneezing reflexes

Reticular Formation

· Diffusely scattered neurons throughout the area of medulla, pons, and midbrain

Reticular Formation Function

· Receives afferent projections providing all types of sensory input and is essential for arousal and maintaining wakefulness

· Contains center for facilitating or inhibiting stretch reflexes

· Controls cyclic activities such as sleep-wake cycle

Ventricles of the Brain

canals in the brain that contain cerebrospinal fluid
: continuous with the central canal of the spinal cord

Four Ventricles of the Brain

1. Two (lateral ventricles) one in each hemisphere
2. One (third ventricle) in the diencephalon
3. One (fourth ventricle) anterior to the cerebellum

Meninges of the Brain

Covering of the Brain
: Dura Mater, Arachnoid, Pia Mater

Dura Mater

· outermost dense fibrous tissue consisting of two layers:

A. Endosteal Dura
outermost; forms the internal periosteum of the cranial bones

B. Meningeal Dura
continuous with the epineurium of the spinal nerves

Arachnoid

· Middle meninx (singular)
· A loose, delicate membrane with microscopic appearance of a spider web
· Thin and wispy

Pia Mater

· Inner meninx
· A vascular membrane
· Bound tightly to surface of the brain and spinal cord
· Forms the filum terminale, which anchors spinal cord to coccyx and the denticulate ligaments that attach the spinal cord to the dura mater

Spaces

1. Epidural Space

Epidural Space

· Anesthesia injected
· Contains blood vessels, areolar connective tissue and fat

Subdural Space

· Serous fluid

Subarachnoid Space

· CSF and blood vessels within web-like strands of arachnoid tissue

Cerebrospinal Fluid

Circulates with:
· Ventricles
· central canal of spinal cord
· subarachnoid space of the brain and spinal cord (between arachnoid and pia mater)
· Serves as protective jacket
· Provides buoyancy for brain

What produces CSF?

choroid plexus in ventricles

Choroid Plexus

pouch-like projections of pia mater into ventricles; covered with ependymal cells

Cerebrospinal Fluid

· Circulates from lateral ventricles through foramina of Monro into third ventricles

· Passes through cerebral aqueduct into fourth ventricle (and spinal cord)

· Passes through three foramina into subarachnoid space

· Drains into the superior sagittal sinus

· A separation between endosteal and meningeal dura through arachnoid villi (projections of arachnoid into sinus)

Blood Brain Barrier

· Capillary endothelial cells along with astrocytes and basement membrane

· To be considered when developing drugs

· Endothelial cells have tight junctions between them

· Astrocytes have foot processes that influence capillary permeability

· Basement membrane of endothelium

Responsible for the formation of Blood Brain Barrier?

Foot Process of Astrocytes

CSF Functions:

1. Allows careful selection of what substances can cross to neurons

2. Capillary walls are different
a. Fewer pores
b. Tight junctions
c. Special carriers

3. Water soluble substances do not cross easily
a. Lipophilic molecules can cross

The total volume of CSF in the adult ranges from

140 to 270 ml.

he volume of the ventricles is about

25 ml.

CSF is produced at a rate of

0.2 - 0.7 ml per minute or 600-700 ml per day

Spinal Cord

· Extends from foramen magnum to 2nd lumbar vertebra
· Gives rise to spinal nerves
· Segments of spinal nerves

o Cervical
o Thoracic
o Lumbar
o Sacral

Spinal Cord

Central H-shaped core of gray matter surrounded by white matter

Conus medullaris

tapered inferior end

Cauda Equina

Origins of spinal nerves extending inferiorly from lumbosacral enlargement and conus medullaris

Filum Terminale

Slender extension of pia mater below spinal cord

Dorsal Root Ganglion

Collections of cell bodies of unipolar sensory neurons forming dorsal roots.

Ventral Root Ganglion

Motor neuron cell bodies are in anterior and lateral horns of spinal cord gray matter

: Multipolar somatic motor neurons in anterior (motor) horn

Peripheral Nervous System

the sensory and motor neurons that connect the central nervous system to the rest of the body

Sensory Receptors

- ending of neuron
- separate, specialized cells that detect temperature, pain, touch, pressure, light, sound, odor

Nerve

- bundle of axons and their sheaths
- connects CNS to sensory receptors, muscles and glands

Cranial Nerves

- originate from the brain

Spinal Nerves

- originate from spinal cord

Ganglion

- collection of neuron cell bodies outside CNS

Plexus

- extensive network of axons, sometimes neuron cell bodies, located outside CNS

12 cranial nerves

1. Olfactory
2. Optic
3. Oculomotor
4. Trochlear
5. Trigeminal
6. Abducens
7. Facial
8. Vestibulocochlear
9. Glossopharyngeal
10. Vagus
11. Accessory
12. Hypoglossal

Mnemonics:
Oh, Oh, Oh, To Touch And Feel A Girls Velvet So Heavenly!

Function: Sensory or Motor
Some Say Mary Money But My Brother Says Big Brain Matter More

Olfactory Nerve

smell

Optic Nerve

vision

Oculomotor Nerve

Motor to four of six eye extrinsic muscles and upper eyelid; Parasympathetic: constrict pupil

Trochlear Nerve

Motor to one extrinsic eye muscle

Trigeminal Nerve

Sensory to face and teeth; Motor to muscle of mastication (chewing)

Abducens Nerve

Motor to one extrinsic eye muscle

Facial Nerve

Sensory: Taste; Motor to muscle of facial expression; Parasympathetic to salivary and tear gland

Vestibulocochlear Nerve [Auditory]

Hearing and balance

Glossopharyngeal

Sensory: taste and touch to back of tongue; Motor to pharyngeal muscles; Parasympathetic to salivary glands

Vagus

Sensory to pharynx, larynx, and viscera; Motor to palate, pharynx and larynx; Parasympathetic to viscera of thorax and abdomen

Accessory [Spinal Accessory]

Motor to two neck and upper back muscle

Hypoglossal

Motor to tongue and muscles

Structure of Peripheral Nerve

Consist of:
1. Axon Bundles
2. Schwann Cells
3. Connective Tissue

Nerve Connective Tissue

1. Endoneurium
2. Perineurium
3. Epineurium

Endoneurium

Surrounds individual neurons

Perineurium

Surrounds axon groups to from fascicles

Epineurium

Surrounds the entire nerve

Peripheral Nervous System Classification

Sensory

Motor
A. Somatic Nervous System
B. Autonomic Nervous System
1. Sympathetic Nervous System
2. Parasympathetic Nervous System

Division of Peripheral Nervous System

Sensory (Afferent):
Motor (Efferent):