Nervous System
AP Biology
Ch. 48
Ms. Haut
Function of Nervous System

Sensory Input
– Conduction of signals from sensory receptors

Integration
– Carried out by Central Nervous System (CNS)


Brain and spinal cord
Motor Output
– Carried out by Peripheral Nervous System (PNS)
– Conduction of signals 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
 Interneurons: integrate sensory input and
motor output (carry stimuli in the brain and
spinal cord)
 Motor Neurons: convey impulses from CNS
to effector cells in muscles or glands
 Glial cells: support, protect, and nourish
neurons
Structural Diversity of Neurons
Overview of Vertebrate Nervous System
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
http://bio.rutgers.edu/~gb102/lab_5/103ar.html
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
Graded Potentials
“All-or-none event”
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
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
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.
Organizations of Invertebrates
CNS
Without CNS
CNS
(PNS)
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
visceral (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
Sleep and Arousal

Controlled by several centers in the cerebrum and
brainstem
 Reticular formation: neurons that pass through the
brainstem
– Reticular activating system--regulates sleep and arousal
– Increased input to cortex, increases alertness

Medulla and pons
– Nuclei stimulated induces sleep
– Serotonin may activate sleep centers
Lateralization, Language, and
Speech

Association areas of cerebral cortex are
lateralized (specialized functions)
 Left hemisphere
– Speech, language, calculation, and rapid serial
processing of details

Right hemisphere
– Overall context, spatial perception, and creative
abilities
Emotions

Limbic system-functional group of nuclei and
interconnecting axon tracts in the CNS
– Includes parts of the thalamus and hypothalamus, and
portions of the cerebral cortex
– Linked to areas of cerebral cortex involved with
complex learning, reasoning, and personality

Amygdala-prominent component of limbic system
– Major organizer of emotional information
– Plays role in memory association