CHAPTER 7 Nervous system Notes

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Transcript CHAPTER 7 Nervous system Notes

CHAPTER 7
NERVOUS SYSTEM
ORGANS AND DIVISIONS OF THE
NERVOUS SYSTEM

Central Nervous System (CNS):


Peripheral Nervous System (PNS):


Organs: Brain and spinal cord
Organs: All Nerves
Autonomic Nervous System (ANS):

Organs: Motor neurons
CELLS OF THE NERVOUS SYSTEM
 2 Types of cells found in the nervous
system:
 1.
NEURONS: nerve cells
Parts:
cell body, dendrites and axon
3 types: sensory, motor and interneurons
 2.
GLIA: specialized connective tissue
Glia means glue. Holds the functioning
neurons together to protect them.
NEURONS
 Motor neurons transmit impulses away from the
spinal cord and brain to muscle and glandular
epithelial tissue.
 Also
called efferent neurons.
 Interneurons conduct impulses form sensory
neurons to motor neurons.
 Also
called central or connecting
neurons.
 Sensory neurons transmit impulses to the spinal
cord and brain from all parts of the body
 Also
called afferent neurons.
STRUCTURE OF NEURON
 AXON: is surrounded by segmented
wrapping called myelin.
- Myelin is a white, fatty substance by
Schwann cells that wrap around some
axons outside the CNS.
- These fibers are called myelinated
fibers
GLIA
 Glia or neuroglia: They are special types of supporting
cells
- Function: is to hold neurons together and protect
them. - Vary in size and shape:
* Large cells look like stars: astrocytes
* Smaller cells are Microglia
* Oligodendrocytes: helps hold fibers together, produce
the fatty myelin sheath that envelops nerve fibers in the
brain and spinal cord
NERVES
 Nerve is a group of peripheral nerve
fibers (axons) bundled together like
the strands of a cable.
 Myelin is found on nerves and is
white.
 Nerves are called white matter of the
PNS and also the CNS.
 Unmyelinated axons and dendrites
are called gray matter. (because of
gray color)
WHITE AND GRAY MATTER
REFLEX ARC
 Nerve impulses are conducted from receptors to
effectors over neuron pathways known as Reflex
arcs.
 This results in a reflex. (a contracted muscle or
secretion from a gland)
 2 types of reflex arcs:
- two-neuron arcs: spinal cord and motor neuron
- three-neuron arcs: sensory neurons, interneurons
and motor neurons
RECEPTORS
 Impulse conduction normally starts
in the receptors.
 Found at the beginning of the
dendrites of sensory neurons
 Located in the tendons, skin or
mucous membranes.
MS (MULTIPLE Sclerosis)
DAMAGE TO MYELIN
 Hard lesions replace the
destroyed Myelin
 As the myelin is lost,
nerve conduction is
impaired
 Causing weakness, loss in
coordination, visual
impairment, speech
disturbances
 No known cure, occurs
most in women ages 2040.
Synapse
 A microscopic space from the axon ending of one
neuron to the dendrite of another neuron.
 The nerve impulse stops, chemicals are sent across
the gap, the impulse continues alone the dendrites.
Neurotransmitters
 Chemicals by which neurons communicate.
 Specific neurotransmitters are released in specific
pathways.
 Some help us sleep, make us happy, make us more
energetic, some inhibit pain
CNS (CENTRAL NERVOUS SYSTEM)
Spinal Cord and Brain
 4 Divisions of the brain:
 Brainstem
Medulla
Oblongata
Pons
Midbrain
 Cerebellum
 Diencephalon
Hypothalamus
Thalamus
 Cerebrum
.
BRAINSTEM
* Medulla
Oblongata: largest part of
the brainstem.
- extension of the spinal cord
- Location: lies below the pons and the
midbrain
- Functions: reflex center (control
heartbeat, respiration and blood
vessel diameter)
DIENCEPHALON
 Hypothalamus:
- Structure: consists mainly of the posterior pituitary
gland, pituitary stalk and gray matter.
- Function: Acts as the major center for
controlling the ANS. (function of internal
organs)
- Controls hormone secretion
- Centers for controlling appetite, wakefullness and
pleasure
DIENCEPHALON
 THALAMUS:
- Structure: dumbbell shaped mass
of gray matter in each cerebral
hemisphere
- Function: relays sensory impulses
to cerebral cortex
- Produces emotions of
pleasantness and unpleasantness
associated with sensation
CEREBELLUM
 Second largest part of the brain
 Structure: Lies under the occipital
lobe of the cerebrum
 - composed of gray matter in outer
layer and white matter in the inner
layer
• Function: helps control muscle
contractions to produce coordinated
movements.
• Also, maintain balance, move
smoothly and sustain normal posture
CEREBRUM
 Largest part of the brain
 Structure: Structures: Series of ridges and
grooves
-Ridges are called convolutions or Gyri
-Grooves are called Sulci (deepest sulci are called
fissures)
-Divided into two halves- Hemispheres
-Hemispheres connected by the Corpus callosum
CEREBRUM
 HEMISPHERES: Divided into lobes
 Lobes are named after bones that lie over them.
CEREBRUM
 Function: mental process of all types
 Sensations
 Consciousness
 Thinking
 Memory
 Willed Movements
Page 177, second paragraph
Cerebrum
 Specific areas have specific functions
 Temporal lobe’s auditory areas interpret incoming nervous
signals as specific sounds
 Visual area of the occipital lobe helps you understand and
identify images
 If a specific part of the brain is damaged, for example
the Primary Taste Area, you would not be able to
taste things.
__________CEREBRUM
SPINAL CORD
 Structure: Outer part composed of white
matter
- Interior part composed of gray matter
 Function: center of all spinal cord
reflexes
- sensory tracts conduct impulses to the
brain.
- motor tracts conducts impulses from
the brain
Cutting the Cord
 Completely severing the spinal cord produces a loss
of sensation for all areas below the cut, called
anesthesia.
 It also produces a loss of the ability to make
voluntary movements, called paralysis.
Peripheral Nervous System (PNS)
Cranial and Spinal Nerves
 Connect the Brain and Spinal Cord to
Peripheral structures like skin and
muscles.
 Cranial Nerves:
- 12 pairs of cranial nerves
- Functions vary
- see diagram on page 187 and chart on 188 for
function and location (you will need to know
number, name, function)
SPINAL NERVES
 Structure: contain dendrites of sensory
neurons and axons of motor neurons
 Function: conduct impulses necessary for
sensations and voluntary movements
 Dermatones: skin areas that are supplied
by a single spinal nerve
Autonomic Nervous System (ANS)
 Structure: Consists of motor neurons that




conduct impulses from spinal cord or brainstem to:
1. Cardiac Muscle tissue
2. Smooth muscle tissue
3. Glandular epithelial tissue
Function: regulate involuntary functions
- heartbeat, contractions of the stomach and
intestines and secretions by glands
2 Divisions of ANS
 1. Sympathetic nervous system:
-Structure: dendrites and cell bodies
located in gray matter of the thoracic and
upper lumbar segments of the spinal cord
-Function: serves as the emergency or
stress system during strenuous exercise
and strong emotions (hate, anger, fear or
anxiety)
- controls the “ fight or flight”
response
2 Divisions of ANS
 2. Parasympathetic Nervous System:
 Structure: Neurons are located in gray
matter of the brainstem and sacral
segments of the spinal cord.
 Function: dominates control of many
visceral effectors under normal
everyday conditions (bladder,
intestines, lung)
Autonomic Neurotransmitters
 Each division of the ANS signals its effectors with a
different neurotransmitter.
 This is how an organ can tell which division is
stimulating it.

Ex. The heart responds to acetylcholine from the
parasympathetic division by slowing down. If norepinephrine,
from the sympathetic division, is present, the heart speeds up.
ANS as a Whole
 Regulates the body’s autonomic
functions in ways that maintain
HOMEOSTASIS
 Many visceral effectors are effected by
both sympathetic and parasympathetic
divisions.