Download Nervous System

Nervous System
Biology
Ch. 42
Ms. Haut
Function of Nervous System

Sensory Input
– Signals received by sensory receptors in dermis of skin
or internal organ systems

Integration
– Carried out by Central Nervous System (CNS)


Brain and spinal cord
Motor Output
– Carried out by Peripheral Nervous System (PNS)
– Signals are sent to muscle or gland cells
– Carry out body’s responses to stimuli
Animal Nerve Cells

Nerves: rope-like bundles of extensions of
neurons, tightly wrapped in connective
tissue
 Neurons: functional unit of the nervous
system
Functional Organization of
Neurons

Sensory Neurons: relay information
(stimuli) from the external and internal
environments to CNS
 Motor Neurons: convey impulses from CNS
to cells in muscles or glands
Overview of Vertebrate Nervous System
Neural Signals

Nerve impulse is an electrical signal that
depends on the flow of ions across the
plasma membrane of a neuron
Membrane Resting Potential
Cell is said to be polarized
Action Potential

A nerve impulse is generated when the
difference in electrical charge disappears
 Occurs when a stimulus contacts the tip of a
dendrite and increases the permeability of
the cell membrane to Na+ ions
 Cell is said to be depolarized
Regulation of Action Potential
Propagation
of the Action
Potential

After the wave
of depolarization
has passed, the
neuron
reestablishes the
difference in
charges by
pumping K+ out
of the cytoplasm
Action Potential
Nerve Impulse
Saltatory Conduction
Synapses

Nerve impulses pass down the dendrite,
through the cell body, and down the axon.
 At the end of the axon, the signal reaches a
fluid-filled space (synapse) separating the
end of the axon from the dendrite of the
next neuron.
 Neuromuscular junction: synapse located at
the junction of a neuron and muscle fiber
Neuron Circuitry

Simplest neural circuit involves synapses
between 2 neurons, a sensory neuron and a
motor neuron
 Result is often an automatic response called
a reflex
The Knee-jerk Reflex
Chemical Synapse
Chemical
Synapse
MAJOR NEUROTRANSMITTERS AND THEIR EFFECTS
Acetylcholine
(ACh)
Generally
excitatory
Affects arousal, attention, memory,
motivation, movement. Too much: spasms,
tremors. Too little: paralysis, torpor.
Dopamine
Inhibitory
Inhibits wide range of behavior and
emotions, including pleasure. Implicated in
schizophrenia and Parkinson's disease.
Serotonin
Inhibitory
Inhibits virtually all activities. Important
for sleep onset, mood, eating behavior.
Norepinephrine
Generally
excitatory
Endorphins Inhibitory
Affects arousal, wakefulness, learning,
memory, mood.
Inhibit transmission of pain messages.
Vertebrate
Nervous
System
Autonomic Nervous System

Works on an involuntary basis
 2 subdivisions
Parasympathetic
Sympathetic
Return body to normal
after an emergency
Heart rate slows, pupils
constrict, blood vessels
dilate
Prepare body for
emergency
Increase heart rate,
constricted blood
vessels, pupils dilate
Roles of
Parasympathetic
and Sympathetic
Divisions of the
Autonomic
Nervous System
Structure of Brain
Brainstem

Medulla oblongata
– Contains centers that control
autonomic, homeostatic functions


Breathing, heart and blood vessel activity,
swallowing, vomiting, and digestion
Pons
– Have nuclei in the medulla that regulate breathing centers

Midbrain
– Centers for receipt and integration of sensory information

Coordinates large-scale body movements such as
walking
Cerebellum

Primary function is
coordination of movement
 Receives information about
position from joints and length of muscles,
as well as auditory and visual systems
 Plays role in learning and remembering
motor responses (hand-eye coordination)
Thalamus and
Hypothalamus

Thalamus
– Main input center for sensory information going to
cerebrum
– Receives input from cerebrum to regulate emotion and
arousal

Hypothalamus
– Source of posterior pituitary hormones and releasing
hormones that act on anterior pituitary
– Regulates body temp, thirst, hunger, other basic
survival mechanisms
– Plays role in sexual response and mating behaviors,
fight-or-flight response, and pleasure
Structure and Function of
Cerebrum
Drug Affects
Cocaine binds to the
dopamine transporter
and prevents re-uptake
of dopamine.
By inhibiting dopamine reuptake, it increases
dopamine and the
pleasure sensation
Drug Affects

Nicotine
– Addictive stimulant
– Mimics action of acetylcholine which controls
central functions of brain
– Continued smoking, smoker’s brain adjusts
– Withdraw nicotine and body becomes out of
balance (“shakes”)
– Smoking associated with lung cancer, heart
disease, and respiratory disorders
Drug Affects

Alcohol
– Depressant
– Changes shape of receptor proteins of neurons
 Become more or less sensitive to regular stimuli
– Effects normal brain function
 Slows motor skills and coordination
– Excessive drinking can lead to malnutrition,
abnormalities in circulatory system, liver
damage (cirrhosis)