Download The Nervous System

The Nervous System
Functions of the Nervous System
 Respond to internal and external stimuli
 Transmit nerve impulses to and away from CNS
 Interpret nerve impulses at the cerebral cortex
 Assimilate experiences in memory and learning
 Initiate glandular secretions and muscle contraction
 Program instinctual behavior
Organs and Divisions of the
Nervous System
 Central nervous system (CNS)—
brain and spinal cord
 Peripheral nervous system
(PNS)—all nerves
 Autonomic nervous system
(ANS) – sympathetic and
parasympathetic
Cells of the Nervous System
 Neurons
 Consist of three parts
 Cell body of neuron—main
part
 Dendrites—branching
projections that conduct
impulses to cell body of
neuron
 Axon—elongated projection
that conducts impulses
away from cell body of
neuron
Cells of the Nervous System
 Neurons
 Neurons classified according to function or
direction of impulse
 Sensory neurons: conduct impulses to the spinal cord and
brain; also called afferent neurons
 Motor neurons: conduct impulses away from brain and
spinal cord to muscles and glands; also called efferent
neurons
 Interneurons: conduct impulses from sensory neurons to
motor neurons; also called central or connecting neurons
Nerves
 Nerve—bundle of peripheral axons
 Tract—bundle of central axons
 White matter—brain or cord tissue composed primarily of
myelinated axons (tracts)
 Gray matter—brain or cord tissue composed primarily of
cell bodies and unmyelinated fibers
Nerves
 Nerve coverings—fibrous connective tissue
 Endoneurium—surrounds individual fibers within a nerve
 Perineurium—surrounds a group (fascicle) of nerve fibers
 Epineurium—surrounds the entire nerve
Reflex Arcs
 Nerve impulses are conducted from receptors to
effectors over neuron pathways or reflex arcs
 Conduction by a reflex arc results in a reflex (i.e.,
contraction by a muscle or secretion by a gland)
 The simplest reflex arcs are two-neuron arcs—
consisting of sensory neurons synapsing in the spinal
cord with motor neurons; three-neuron arcs consist of
sensory neurons synapsing in the spinal cord with
interneurons that synapse with motor neurons
Reflex Arcs
Nerve Impulses
 Self-propagating wave of
electrical disturbance that
travels along the surface of a
neuron membrane; sometimes
called action potentials
Nerve Impulses
 Mechanism
 At rest, the neuron’s membrane is slightly positive on the
outside—polarized—from a slight excess of Na+ on the outside
 A stimulus triggers the opening of Na+ channels in the plasma
membrane of the neuron
 Inward movement of Na+ depolarizes the membrane by
making the inside more positive than the outside at the
stimulated point; this depolarization is a nerve impulse
(action potential)
 The stimulated section of membrane immediately
repolarizes, but by that time the depolarization has already
triggered the next section of membrane to depolarize, thus
propagating a wave of electrical disturbances
(depolarizations) all the way down the membrane
The Synapse
 Place where impulses are transmitted from one
neuron to another (the postsynaptic neuron)
 Synapse made of three structures—synaptic knob,
synaptic cleft, and plasma membrane
 Neurotransmitters bind to specific receptor molecules
in the membrane of a postsynaptic neuron, opening
ion channels and thereby stimulating impulse
conduction by the membrane
 https://youtu.be/Iws8w6NpsGg - easier video
 https://youtu.be/L41TYxYUqqs- Bozman science
Neurotransmitters
Actions
Disorder Involving It
Acetylcholine
-Triggers muscle contraction and
stimulates the excretion of certain
hormones
-In CNS: involved in wakefulness,
attentiveness, anger, aggression, etc.
Alzheimer’s disease (lack
of acetylcholine in
certain areas of the
brain)
Dopamine
-Controls movement and posture,
modulates mood, and plays a central role
in positive reinforcement and dependency
Parkinson’s disease (loss
GABA (gammaaminobutyric
acid)
-Contributes to motor control, vision, and
many other cortical functions; regulates
anxiety
Drugs that increase GABA in
the brain are used to treat
epilepsy and Huntington’s
disease
Glutamate
-Learning and memory
Thought to be associated with
Alzheimer’s disease, whose first
symptoms include memory
malfunctions
Norepinephrine
-Attentiveness, emotions, sleeping, dreaming,
and learning; also released as a hormone into
the blood, where it causes blood vessels to
contract and heart rate to increase
Mood disorders like
manic depression
Serotonin
-Regulating body temperature, sleep,
mood, appetite, and pain
Depression, impulsive
behavior, and
aggressiveness
of dopamine in certain
areas of the brain)
Central Nervous System (CNS)
 Brain
 Divisions
 Brainstem
 Cerebellum
 Cerebrum
 Spinal Cord
Brain - Brainstem
 Consists of three parts, named in ascending order: medulla
oblongata, pons, and midbrain
 Structure—white matter with bits of gray matter scattered
through it
 Functions
 All three parts of brainstem are two-way conduction paths
 Sensory tracts in the brainstem conduct impulses to the higher
parts of the brain
 Motor tracts conduct from the higher parts of the brain to the
spinal cord
 Many important reflex centers lie in the brainstem
Brain - Brainstem
 Medulla oblongata
 Connects brain to spinal cord
 Regulates breathing, heart and
blood vessel function, digestion,
sneezing, and swallowing
 Pons
 Helps relay messages from the cortex and the cerebellum
 Midbrain
 Associated with vision, hearing, motor control,
sleep/wake, arousal (alertness), and temperature
regulation
Brain - Cerebellum
 Second largest part of the human
brain
 Helps control muscle contractions to produce
coordinated movements so that we can maintain
balance, move smoothly, and sustain normal postures
 Recent evidence shows the coordinating effects of the
cerebellum may be more extensive, also assisting the
cerebrum and other regions of the brain
Brain - Cerebrum
 Largest part of the human brain
 Outer layer of gray matter is the cerebral cortex;
made up of lobes; composed mainly of dendrites
and cell bodies of neurons
 Interior of the cerebrum composed mainly of white
matter (i.e., nerve fibers arranged in bundles called
tracts)
 Functions of the cerebrum—mental processes of all
types, including sensations, consciousness, memory,
and voluntary control of movements
Brain – Lobes of the Cerebrum
 Frontal Lobe
 Personality, behavior,
emotions
 Judgment, planning, problem
solving
 Speech: speaking and writing
(Broca’s area)
 Body movement (motor strip)
 Intelligence, concentration,
self awareness
 Occipital Lobe
 Interprets vision (color, light,
movement)
 Parietal Lobe
 Interprets language, words
 Sense of touch, pain,
temperature (sensory strip)
 Interprets signals from
vision, hearing, motor,
sensory and memory
 Spatial and visual perception
 Temporal Lobe
 Understanding language
(Wernicke’s area)
 Memory
 Hearing
 Sequencing and organization
Deep Structures of the Brain
 Hypothalamus gland: hunger, thirst, sleep, and sexual response,
regulates body temperature, blood pressure, emotions, and
secretion of hormones
 Pituitary gland: known as the “master gland,” it controls other
endocrine glands in the body; produces many hormones
 Pineal gland: regulates the body’s internal clock and circadian
rhythms by secreting melatonin
 Thalamus: serves as a relay station for almost all information that
comes and goes to the cortex
 Limbic system (includes hypothalamus, amygdala, and
hippocampus)
 Amygdala: emotional reactions
 Hippocampus: memory
 Corpus callosum: allows for communication between hemispheres
Brain Myths: Fact or Fiction?
1. You only use 10% of your brain.
2. A person can be either left-brained or right-brained.
3. Each person’s brain has a set learning style.
4. Some people are able to multitask very well.
Testing your memory
 I will recite a list of 10 words
 Do not record them in any way
 Try to remember as many of them
as you can (in order if possible)
 You will then be able to write them
down to see what you were able to
remember
 Sunflower
ball
 Red
money
 Chair
rain
 Woman
 Globe
 Comb
 theater
Spinal Cord
 Columns of white matter, composed of
bundles of myelinated nerve fibers,
form the outer portion of the H-shaped
core of the spinal cord; bundles of axons
called tracts
 Interior composed of gray matter made up
mainly of neuron dendrites and cell bodies
 Spinal cord tracts provide two-way conduction paths—
ascending and descending
 Spinal cord functions as the primary center for all spinal cord
reflexes; sensory tracts conduct impulses to the brain, and
motor tracts conduct impulses from the brain
Coverings and fluid spaces of the
brain and spinal cord
 Coverings
 Cranial bones (skull) and vertebrae
 Cerebral and spinal meninges
 Fluid spaces
 Subarachnoid spaces of meninges
 Central canal inside cord
 Ventricles in brain
 Fluid
 Cerebrospinal fluid – cushions and provides immune protection
Peripheral Nervous System (PNS)
 Cranial nerves
 12 pairs—attached to undersurface of the brain
 Connect brain with the neck and structures in the thorax
and abdomen
 Spinal nerves
 31 pairs—contain dendrites of
sensory neurons and axons of
motor neurons
 Conduct impulses necessary for
sensations and voluntary
movements
 After exiting the vertebral column,
they split, combine, and split again
forming a plexus (there are 4)
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

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Cervical plexus
Brachial plexus
Lumbar plexus
Sacral plexus
Autonomic Nervous System
 Responsible for controlling unconscious bodily
functions (heartbeat, breathing, digestion)
 Composed of two divisions: the sympathetic system
and the parasympathetic system
Autonomic Nervous System
 Sympathetic nervous system
 Serves as the emergency or stress system, controlling
visceral effectors during strenuous exercise and when
strong emotions (anger, fear, hate, or anxiety) are elicited
 Group of changes induced by sympathetic control is called
the fight-or-flight response
 Parasympathetic nervous system
 Dominates control of many visceral effectors under
normal, everyday conditions