Download Chapter 7 Nervous System Every conscious action is governed by

Chapter 7 Nervous System
Every conscious action is governed by the nervous system
Functions
 Communication between distant parts of the body
 Collection and integration of stimuli (both internal and external
 Formation and initiation of appropriate response
 Responsible for very rapid responses
 Crucial role in maintaining homeostasis
 Works in a concerted effort with the endocrine system (slower, longer-lasting
responses)
The nervous divisions
 2 divisions:
o
Central nervous system (CNS): Brain and spinal cord
o
Peripheral nervous system (PNS): All of the neurons that extend from the
CNS
How the two work together
 Information is passed from sensory receptors to PNS
o
Special senses (sight, hearing, smell, taste)
o
General sensory receptors (touch, light, external heat, pain)
o
Visceral receptors (monitoring internal organ function)
 Information moves from PNS to CNS
 Information is processed by the CNS and the appropriate response is determined
 Motor response is sent from CNS via PNS to appropriate muscles or glands
The peripheral nervous system
 Divided into 2 systems:
o
Somatic
o
Autonomic
 The PNS: Somatic division
o
Serves the skin, skeletal muscles, and tendons
o
Mainly involved with conscious actions but also responsible for reflex
responses
o
Automatic responses are called reflexes
 The PNS: Autonomic division
o
Regulates the activity of involuntary muscles (cardiac and smooth) and
glands to maintain homeostasis
o
Divided into 2 divisions:
 Sympathetic - coordinates the body for the “fight or flight” response
by speeding up metabolism, heart rate, and breathing while downregulating other functions
 Parasympathetic - counters the sympathetic system by promoting a
relaxed state by slowing metabolism, heart rate, and breathing and
returning other functions to normal
The nervous system
 2 cell types: neurons and neuroglia
 Expanding on neurons
o
3 types of neurons:
o
Sensory – take impulses from sensory receptor to CNS
o
Interneurons – receive information in the CNS and send it to a motor
neuron
 These essentially connect the sensory and motor neurons
o
Motor – take impulses from the CNS to an effector (i.e. gland or muscle
fiber)
 Nerve impulses move from the dendrite through the cell body and then down the
axon
 From the axon terminus, the signal is transferred to the next neuron
 Nerve impulses
 Neurons function because without any impulse, they already have a resting potential
o
This requires creating a charge imbalance across the cell membrane
o
The charge imbalance is generated by the Na+/K+ pump (active transport
requiring ATP)
o
The ions remain in place because of gated channels
o
When neurons “fire” in response to signals, there is a rapid reversal of the
charge differential across the membrane
o
Nerve impulses move from the dendrite through the cell body and then
down the axon
o
From the axon terminus, the signal is transferred to the next neuron
 Neurotransmitters
o
Between adjacent neurons are small spaces called synapses
o
Neurotransmitters are released by one neuron and received by the next
neuron
 Synaptic integration
o
Integration is the summation of the inhibitory and excitatory signals
received by a postsynaptic neuron
o
This occurs because a neuron receives many signals
The central nervous system
o Consists of the brain and the spinal cord
o Both are protected by:
o
Bones – skull and vertebral column
o
Meninges – 3 protective membranes that wrap around CNS
o
Cerebral spinal fluid (CSF) – space between meninges is filled with this
fluid that cushions and protects the CNS
o Both are made up of 2 types of nervous tissue:
o
Gray matter – contains cell bodies and nonmyelinated fibers
o
White matter – contains myelinated axons
The CNS: Brain
Four major parts:
1. The brain stem
o Midbrain – relay station between the cerebrum and the spinal cord or cerebellum;
reflex center for sneezing, hiccuping, swallowing, coughing
o Pons – a bridge between the cerebellum and the CNS; regulates breathing rate; reflex
center for head movements
o Medulla oblongata – reflex centers for regulating breathing, heartbeat, and blood
pressure
2. Diencephalon
Includes the:
Hypothalamus – helps maintain homeostasis (responds to or initiates hunger, sleep,
thirst, body temperature, and water balance) and controls the pituitary gland
Thalamus – 2 masses of gray matter that receive all sensory input except smell;
involved in memory and emotions; also visual and auditory startle reflexes
Pineal gland – secretes melatonin that controls our daily rhythms
3. Cerebellum
o Receives and integrates sensory input from the eyes, ears, joints, and muscles about
the current position of the body
o Functions
o
Maintains posture
o
Coordinates voluntary movement
o
Allows learning of new motor skills (i.e. playing the piano or hitting a
baseball)
4. Cerebrum – the lobes
o Cerebrum – largest portion of the brain
o Divided into 4 lobes/hemispheres:
o
Frontal lobe: primary motor area and conscious thought
o
Temporal lobe: primary auditory, smell, and speech area
o
Parietal lobe: primary somatosensory and taste area
o
Occipital lobe – primary visual area
o Cerebrum – the cerebral cortex
o
Cerebral cortex – thin, outer layer of gray matter:
o
Primary somatosensory area – sensory information from skeletal muscle
and skin
o
Primary motor area – voluntary skeletal muscle
o
Association areas – integration occurs here
o
Processing centers – perform higher level analytical functions, includes
areas involved in speech
Higher mental functions
o Learning – what happens when we recall and use past memories
o Memory – ability to hold a thought or to recall past events
o Short-term memory – retention of information for only a few minutes
o Long-term memory – retention of information for more than a few minutes and
includes the following:
o
Episodic memory – persons and events
o
Semantic memory – number and words
o
Skill memory – performing skilled motor activities (i.e. riding a bike)
o
Language – depends on semantic (words and their meanings) memory
Drugs and drug abuse
o Drugs have two general effects on the nervous system - affect the limbic system or
promote the action of a certain neurotransmitter
o Most drug abusers take drugs that affect dopamine and thus artificially affect the
reward circuit to the point they ignore basic physical needs in favor of the drug
o Nicotine causes the release of dopamine