Transcript Nervous System Notes

Nervous System
Northwest Rankin High School
Human A&P
Functions of the Nervous System
Monitors changes inside and outside of
the body. Changes are stimuli and
gathered info is called sensory input
 Integration: processes the sensory input
and makes decisions about what should
be done
 Affects a response by activating muscles
or glands, motor response
 Video Clip

Structural Organization
Central Nervous
System (CNS)
Brain and Spinal Cord

Structural Organization

Peripheral Nervous
System (PNS)
Nerves that extend from
the brain and spinal
cord
Nervous System Overview
Nervous System
Composed of 2 types of neural
tissue

Neurons – are
specialized to react to
physical and chemical
changes in their
surroundings.

Neuroglial cells –
surround the neurons
and nourish neurons
and perhaps send
and receive
messages.
Neuron
Neurons
Nerve cells that are highly specialized to
transmit messages (nerve impulses) from
one part of the body to another
 Video Clip

Parts of a neuron
Cell Body – contains nucleus
 2 types of processes or fibers extending
from the body

1. Dendrite –
 receives stimuli
 may have hundreds per neuron
 conduct currents toward the cell body
Neurons Cont.
2. Axon
 neurons
have only one
 Conduct nerve impulses away from the cell
body
 Axons branch to form axonal terminals
 Neurotransmitters are released when
impulses reach the terminals
 Synaptic cleft separates one neuron from the
next
THE NEURON
d
cb
a
d
d
The cell body is the portion of the nerve cell that surrounds the
nucleus. Multipolar neurons have several branches arising form the
cell body (cb). There is usually one axon (a) and many dendrites (d).
Dendrites carry nerve impulses to the cell body. The axon is
designed to carry nerve messages away from the cell body.
Neurons cont.

Myelin – mass of
white lipid material
that insulates the
axon. These are
called Schwann cells.
Gaps between these
cells are known as
nodes of Ranvier.
Disease Example

Multiple Sclerosis –
myelin sheaths are
damaged and
hardened which
causes the person to
lose the ability to
control muscle
movement.
Neuron Classification

Sensory (afferent)
neurons – carry
impulses from the
sensory receptors in
the organs and skin to
the CNS

Motor (efferent)
neurons – carry
impulses from the
CNS to the muscles
or glands

Association
(interneuron) neurons
connect motor and
sensory neurons
3 Neuron Structures

Multipolar Neuron
•
Has many processes
•
•
Including dendrites and
axon
most common type
3 Neurons Cont.

Bipolar Neuron
•
Two processes –
•
•
1 axon and 1 dendrite
Rare in adults, but
found in some special
sense organs
Neurons Cont.

Unipolar Neuron
•
Single process
emerging from the cell
body
Neuroglia

Many types of cells
that support, insulate,
and protect delicate
neurons.
Types of Neuroglia
Astrocytes – form a barrier between
capillaries and neurons
 Microglia – phagocytes that dispose of
debris like dead brain cells and bacteria.
 Ependymal Cells – line the cavity of the
brain and spinal cord.
 Oligodendrocytes – help to form the
myelin sheath

Neuroglia differs from Neurons
Resemble neurons structurally, but are not
able to transmit nerve impulses
 Never lose the ability to divide like
neurons. Most brain tumors are formed by
glial cells.

Physiology of Nerve Tissue
2 types

Nerve Impulses have 2 major functions
1.
Irritability: ability to respond to a
stimulus and convert it into a nerve
impulse
Conductivity: ability to transmit the
impulse to other neurons, muscles, or
glands.
2.
Conductivity

Neurotransmitters
allow the impulse to
continue between
neurons
Reflex Arc


Reflexes are rapid, predictable, and
usually involuntary responses to stimuli
2 types
1.
2.
Autonomic - INVOLUNTARY
Somatic - VOLUNTARY
Pathway of Reflex Arc
1.
2.
3.
4.
5.
Receptor – reacts to stimulus
Afferent Neuron – carry impulse to CNS
Integration – synapse between afferent
and efferent neuron
Efferent neuron – carry impulse to
muscles or glands
Effector – muscles or glands to be
stimulated
Central Nervous System
Consists of the brain and spinal cord
 The brain weighs a little over 3 pounds
and is about the size of two fists.
 It looks to be pinkish gray tissue, wrinkled
like a walnut, with a cold oatmeal texture

The Brains 4 Major Regions
Cerebrum
Cerebellum
Brain Stem
1.
2.
3.



Diencephalon
4.




Midbrain
pons
medulla oblongata
Thalamus
Hypothalamus
epithalamus
Video Clip
Cerebrum


Largest portion of the brain
Has 2 cerebral hemispheres (right and left)
connected by the corpus callosum
4 Lobes of the Cerebrum
1.
2.
3.
4.
Frontal
Parietal
Temporal
Occipital
The names of the lobes come from the skull
bones that overlie them.
Cerebral Cortex – Gray Matter


Folded outer
layer of the
cerebral
hemispheres
Gray color
because it
contains cell
bodies
Cerebral Cortex – Gray Matter



Covered by elevated
ridges of tissue called
gyri (gyrus – singular)
and is the gray
matter.
Shallow grooves that
separate the ridges
are called sulci
(sulcus – singular)
Deep grooves are
called fissures
Cerebral Cortex - White Matter


Lies below the
cerebral cortex –
gray matter
Is composed of the
axons of cortical
neurons
Parietal Lobe


Interprets impulses
sent from sensory
receptors
Speech and ability to
use words
Frontal Lobe


Voluntary muscle
control
Problem solving and
planning
Occipital Lobe

Area responsible for
vision
Temporal Lobe


Hearing
Auditory and visual
memory

Hippocampus – short
term memory
Cerebellum


A region of the brain
that plays a vital role
in the coordination of
muscle action
Helps maintain
normal muscle tone
Brain Stem

Midbrain


Pons


Important relay center for visual
and auditory information
Serves as a relay center between
the neurons of the cerebral
hemispheres and those of the
cerebellum. Helps control
breathing.
Medulla Oblongata

Serves as both a relay center and
control center. Helps regulate
heart rate, blood pressure,
breathing, swallowing, and
vomiting
Diencephalon



Thalamus – directs most incoming
signals to the proper region of the
cerebral cortex
Hypothalamus –
 regulation of body temp, water
balance, and metabolism
 directly and indirectly controls
much of the body’s hormone
production. (Pituitary gland of
endocrine system)
 Part of limbic system - emotion
 Thirst, appetite, pain, sex,
and pleasure centers
Epithalamus – includes the pineal
body ( endocrine system) and
choroid plexus (makes CSF)
Protection of the CNS
Bones of the skull and vertebral column
protect the CNS
 Meninges – membranes between bone
and soft tissue.

3 Layers of Meninges



Dura matter – tough
outermost
Arachnoid matter –
middle, web like
Pia matter –
innermost delicate
Cerebrospinal Fluid (CSF)
A watery cushion around the brain and
cord.
 Continually formed and drained to keep a
constant rate.
 Any fluctuation in the in the pressure could
indicate a disorder.

Blood – Brain Barrier
Neurons are kept separate from blood
borne substances
 Metabolic wastes like urea, toxins, and
proteins are prevented from entering brain
tissue.
 Nutrients (like glucose), anesthetics,
water, alcohol, and nicotine all easily pass
through the barrier.

Spinal Cord
Reflex center and
Conduction pathway
Peripheral Nervous System

Nerves and scattered
groups of ganglia
found outside the
CNS.
Functional Classification (PNS)
Afferent (sensory) division: nerve fibers
that convey impulses to the central
nervous system from sensory receptors
located in various parts of the body
 Efferent (motor) division: carry impulses
from the CNS to effector organs, the
muscles and glands

Effector (motor) division


Somatic Nervous system: allows conscious or
voluntary control of skeletal muscles
Autonomic Nervous system: regulates events
that are autonomic or involuntary, such as the
activity of smooth and cardiac muscles and
glands
Autonomic Nervous System

Sympathetic Division




activated by conditions of
physical or emotional stress
fight or flight division
active when an emergency
or threatening situation
arises
Parasympathetic Division


deals with routine
conditions
most active when the body
is at rest and not threatened
in any way
Structure of a Nerve




Bundle of Neuron
fibers outside the
CNS
Each fiber wrapped in
a endoneurium
Group of fibers in a
perineurium
All bound together by
a epineurium
Structure cont.

Classified according to direction of impulse
 Mixed
nerve – carry both sensory and motor
fibers
 Afferent (sensory) – carry impulses to CNS
 Efferent (motor) – carry impulses away from
CNS
Cranial Nerves


12 pair that extend
from the brain to
serve the head and
neck region.
Only exception is the
Vagus nerve which
extends to the thorax
and abdomen
Spinal Nerves

31 pair of nerves
formed by the dorsal
and ventral roots of
the spinal cord
4 Groups of Spinal Nerves
 Cervical:
Diaphragm and muscles of neck
 Brachial: serves the arms
 Lumbar: serves the lower abdomen,
buttocks, and thighs
 Sacral: serves the lower trunk, posterior
surface of thighs, posterior and lateral
aspect of leg and foot