Nervous System

Academic Anatomy & Physiology

The Function To act as the

master controlling and communicating system for the body

Subdivided into CNS & PNS

http://www.agen.ufl.edu/~chyn/age2062/lect/lect_20/nervsys.gif

Cells of the Nervous System 1. Neuroglia

Acts to support neurons Makes up ~ 90% of brain and spinal cord (s.c.) There are 5 different types of

neuroglial cells

Types of Neuroglia A. Astrocytes B. Oligodendrocytes C. Microglial cell D. Ependymal Cells E. Schwann Cells

Assignment Using page 225 in your text, draw

the different types of neuroglia and list their location and function within the nervous system below each drawing

DO NOT draw Schwann cells but do list its location and function

Cells of the Nervous System 2. Neurons

The conducting nerve cell Senses changes in environment,

integrates information, carries out motor responses

Structure: each neuron varies in shape and size, but all have 3 main parts (dendrite, axon and cell body)

Neuron

Neuron Anatomy

A. Dendrite: a process off of the cell body; receives impulses from adjacent neurons & conducts electrical impulses TOWARD the cell body; ~1000/neuron

Neuron Anatomy

B. Axon: aka nerve fiber; acts to transmit impulses AWAY from the cell body; 1 axon/neuron

C. Cell Body: contains the nucleus and metabolic center of the cell

Neuron Anatomy

D. Myelin sheath: made by schwann cells in PNS and oligodendrocytes in CNS; encloses the axon & speeds up the rate of nervous conduction

i. Gray matter: non-myelinated nerve fiber

ii. White matter: myelinated nerve fiber

Neuron Anatomy

E. Nodes of Ranvier: gaps in myelin sheath @ regular intervals; aids in increasing speed of nervous conduction

3 Types of Neurons

1. Afferent (sensory) Neurons: transmit impulses from PNS to CNSi.e. pain receptors and proprioceptors

2. Efferent (motor) Neurons: transmit impulses from CNS to muscles or glands

Motor Neuron

3 Types of Neurons

3. Interneurons (association neurons): located within CNS and conducts impulses between sensory and motor neurons

Nerve Conduction: Distribution of Ions

More Na+ on outside than inside a neuron

More K+ on inside than outside + negatively charged particles

K+ ions permeate through lipid bi-layer more easily than Na+ ions do

Nerve Conduction: Resting Potential Describes a polarized, resting nerve K+ and Na+ follow laws of diffusion Na+/K+ pump maintains the unequal

distribution of these ions across membrane Cell uses energy to keep Na+ out and K+ in

despite natural diffusion Inside of cell is more negative than outside

Nerve Conduction: Depolarization An activated nerve cell; has been

stimulated Na+ specific channels in the

membrane open and Na+ floods into the cell

The charge on the inside of the cell is now LESS negative (more positive)

Nerve Conduction: Repolarization Returning to a resting state K+ specific channels in the membrane

open and K+ floods the outside of the cell This returns the inside of the cell to a

MORE negative (less positive) state Depolarization + Repolarization of a nerve

cell = An Action Potential

Impulse Conduction A wave of bioelectric action potentials

travels the length of a neuron, stimulating adjacent neurons as it goes

Unmyelinated neurons slower than myelinated

Impulses on myelinated neurons seem to jump from one node of Ranvier to the next

The Synapse An action potential is electrical

across the neuron and chemical once it reaches the synaptic cleft

Presynaptic Neurons Have synaptic knobs sensitive to Ca+

When Ca+ is present allow synaptic vesicles within them to release neurotransmitters

The Synapse Neurotransmitters cross the synaptic cleft

and bind to postsynaptic neurons Excitatory Neurotransmitters:

triggers action potential to continue in postsynaptic neuron

Inhibitory Neurotransmitters: lessens the chance of a continuing neurotransmitter

Impaired Conduction The following block nervous

impulses by reducing the membrane permeability to sodium ions Alcohol Sedatives Anesthetics Cold and pressure (slows, does not

impair)

Structural Classifications of Nervous System Central Nervous

System (CNS) Includes brain and

spinal cord Acts as integrating

and command center

Peripheral Nervous System (PNS) Includes nerves

outside of CNS• Spinal nerves• Cranial nerves

Links all parts of body by carrying impulses

Subdivisions of PNS 1.) Somatic system: voluntary

nervous system Contains sensory and motor nerves Makes you aware of the world around

you & allows you conscious control

Subdivisions of PNS 2.) Autonomic System:

involuntary nervous system Consists of motor nerves that carry

impulses to organs, blood vessels and glands

The unconscious or “automatic control”

Subdivisions of Autonomic System A. Sympathetic

division Active during stress heart rate,

respiratory rate and rate of ATP breakdown

B. Parasympa-thetic Division Active during

conditions of normal organ functioning

These 2 divisions often work antagonistically to one another

CNS: The Brain 4 major portions:

Cerebrum: largest; sensory & motor function, higher thought, memory & reasoning

Cerebellum: coordination of skeletal muscles

Diencephalon: sensory information Brain stem: connects parts of nervous

system; controls visceral activities

CNS: Cerebrum Cerebral

Hemispheres Cerebral Cortex Corpus Callosum Gyri Sulci Fissures

CNS: Cerebral Lobes Frontal Lobe: anterior portion

Primary motor area Concentration, planning, problem solving Broca’s Area: motor speech

Temporal Lobe: lateral lobe Interpretation of sensory impulses, memory,

visual & auditory patterns Auditory area Olfactory area

CNS: Cerebral Lobes Parietal Lobe: superior, lateral

lobe Sensory area Understanding speech; using words

Occipital Lobe: posterior lobe Vision Combining visual images; visual

recognition

CNS: Hemisphere Dominance Equal participation in receiving and

analyzing sensory information, controlling skeletal muscles and storing memory

Dominant Hemisphere: ability to understand language 90% of people dominant left side

Nondominant Hemisphere: nonverbal functions, orientation in space, musical patterns, nonverbal visual experiences

CNS: Cerebellum Located inferior to

occipital lobes and posterior to brain stem

Functions in: positioning of limbs, coordinating skeletal movements, maintanance of posture

CNS: Diencephalon Located between cerebral hemispheres;

superior to midbrain Thalamus: central relay center for sensory

impulses; allows awareness of pain, touch & temperature

Hypothalamus: regulates visceral activities; links nervous and endocrine systems

Also holds: optic chiasma, posterior pituitary gland, pineal gland, infundibulum

CNS: Brainstem Connects cerebrum to spinal cord Midbrain: b/n diencephalon and

pons Visual, auditory reflex centers; head

movement for hearing Pons: rounded bulge b/n midbrain

and medulla Relays sensory impulses; helps regulate

breathing

CNS: Brainstem Medulla

Oblongata: from pons to spinal cord Cardiac center,

vasomotor center, respiratory center

CNS: Spinal Cord A continuation of the brain running

from base of brain to 1st or 2nd lumbar vertebrae

Is enclosed within spinal column Is ~ size of thumb except at

enlarged cervical and lumbar plexuses (spinal nerve distribution to upper and lower limbs)

CNS: Spinal Cord Provides a 2-way pathway to and from the

brain Serves as a reflex center Has 31 linear segments giving way to 31

spinal nerves (relay info. from PNS to CNS and vice versa)

Cauda Equina: collection of spinal nerves at the inferior end of the vertebral column

Spinal Cord in Column

http://www.latrobe.edu.au/podiatry/Images/1%20Biomech%20pics/SPINALMECHpics/Spinal%20cord%20diag.GIF

Spinal Cord Cross Section

http://biology.clc.uc.edu/fankhauser/Labs/Anatomy_&_Physiology/A&P202/CNS_Histology/Spinal_Cord/sp_cd_jpgs/Spinal_Cord_PC271478md.JPG

Spinal Cord Cross-Section Gray Matter: unmyelinated

Located in center of cord forming an “H”: divided into horns

Each horn runs a different fiber tract• Posterior Horn: sensory neurons• Anterior Horn: motor neurons• Lateral Horn: motor neurons in autonomic

system

Spinal Cord Cross-Section White Matter: myelinated fibers

Surrounds central gray matter Divided into anterior, posterior and

lateral columns Each column holds longitudinal nerve

tracts•Ascending tracts: carry sensory info to

brain•Descending tracts: carry motor info.

away from brain

Reflex Center Reflex: an extremely rapid response to an

emergency situation Occurs in spinal cord or lower brain; does

not require thinking The Reflex Arc:

Receptor: at end of sensory neuron; can generate an action potential to CNS

Association neurons: receive info. from sensory neuron and routes response to motor neuron

Motor neurons: conduct impulses to effectors

Reflex Arc

Protections of CNS Bone: skull and

vertebral column

Cerebrospinal Fluid (CSF): Made from the blood Forms a watery cushion

that protects tissue from trauma

Changes in composition indicates brain pathology

Protections of CNS Meninges: connective tissue

membranesA. Dura mater: tough outer covering of

brain and s.c.B. Arachnoid mater: middle layerC. Pia mater: inner surface which clings

tightly to surface of brain and s.c.• Subarachnoid space: separates the

arachnoid and pia maters; filled with CSF

Protections of CNS Blood-Brain Barrier

Composed of least permeable capillaries in body

Brain depends on a very constant internal environment

• Allows: water, glucose, and essential amino acids• Disallows: urea, protein and most drugs• Cannot block: fats, respiratory gases and fat soluble

molecules (alcohol, nicotine and anesthetics)