Nervous System Flashcards
The nervous system
obtains sensory information, sensory input,
processes sensory information, integration, and
sends commands to effector cells (muscles) that carry out appropriate responses, motor output.
The central nervous system (CNS)
consists of the
brain and spinal cord (vertebrates).
The peripheral nervous system (PNS)
is located outside the CNS and
consists of
cranial and spinal nerves (axons wrapped in connective tissue)
ganglia (clusters of neuron cell bodies).
Sensory neurons
convey signals from sensory receptors to the CNS.
Interneurons
are located entirely in the CNS,
integrate information, and send it to motor neurons.
Motor neurons
convey signals to effector cells.
Neurons are
cells specialized for carrying signals and
the functional units of the nervous system.
A neuron consists of
a cell body and
two types of extensions or processes that conduct signals,
dendrites and
axons.
Myelin sheaths
form a cellular insulation, and
speed up signal transmission.
myelin is a lipoprotein
myelin accounts for “white matter
Gray Matter
Comprised mostly of neuron cell bodies
Possibly some blood vessels. - A fair amount of
neuroglial cells, cells that support and nourish neurons
membrane potential
At rest, a neuron’s plasma membrane has potential energy—the membrane potential, in which
just inside the cell is slightly negative and
just outside the cell is slightly positive.
The resting membrane potential
The resting membrane potential is the voltage across the plasma membrane of a resting neuron.
The resting potential exists because of
differences in ion concentration of the fluids inside and outside the neuron. Inside the neuron K+ is high and Na+ is low. Outside the neuron K+ is low and Na+ is high.
Resting Membrane Potential is established by….
Na+/K+-ATPase pump
3 Na + ions out for every 2 potassium ions in
Leakiness of membrane to K+
many more K+ leak channels compared to Na+
Intracellular Proteins tend to be negatively charged
“fixed anions”
At Rest = polarized = -70mV
A stimulus
is any factor that causes a nerve signal to be generated. A stimulus
alters the permeability of a portion of the membrane,
allows ions to pass through, and
changes the membrane’s voltage.
Thus, depolarizing the membrane
action potential
A nerve signal, called an action potential, is
a change in the membrane voltage, from the resting potential, to a maximum level, and back to the resting potential.
Action potentials are
self-propagated in a one-way chain reaction along a neuron and are
all-or-none events.
The frequency of action potentials (but not their strength) changes with the strength of the stimulus.
Synapses
are junctions where signals are transmitted between
two neurons or
between neurons and effector cells.
Electrical signals pass between cells at electrical synapses. Found between:
- smooth muscle and cardiac muscle cells
At chemical synapses
the ending (presynaptic) cell secretes a chemical signal, a neurotransmitter,
the neurotransmitter crosses the synaptic cleft, and
the neurotransmitter binds to a specific receptor on the surface of the receiving (postsynaptic) cell.
Some neurotransmitters
excite a receiving cell, and
others inhibit a receiving cell’s activity by decreasing its ability to develop action potentials.
A receiving neuron’s membrane may receive signals
that are both excitatory and inhibitory and
from many different sending neurons.
The summation of excitation and inhibition determines if a neuron will transmit a nerve signal.
Some neurotransmitters can be
excitatory on one tissue and inhibitory on another. Ex: acetylcholine
- Ach is excitatory on skeletal muscle - Ach is inhibitory on cardiac muscle
neurotransmitters
Many small, nitrogen-containing molecules are neurotransmitters.
Acetylcholine
is a neurotransmitter
in the brain and
at synapses between motor neurons and muscle cells.
Biogenic amines
are important neurotransmitters in the CNS and
include serotonin and dopamine, which affect sleep, mood, and attention.
Neuropeptides
consist of relatively short chains of amino acids important in the CNS and
include endorphins, decreasing our perception of pain.
Nitric oxide
is a dissolved gas and
triggers erections during sexual arousal in men.
Many psychoactive drugs
act at synapses and
affect neurotransmitter action.
Caffeine counters the effect of inhibitory neurotransmitters.
Nicotine acts as a stimulant by binding to acetylcholine receptors.
Alcohol is a depressant.
In the vertebrates, the central nervous system (CNS)
consists of the brain and spinal cord and
includes spaces filled with cerebrospinal fluid
forming ventricles of the brain,
forming the central canal of the spinal cord, and
surrounding the brain.
The vertebrate peripheral nervous system (PNS) consists of
cranial nerves,
spinal nerves, and
ganglia.
The PNS can be divided into two functional components
the somatic (motor) system, mostly voluntary, and the autonomic nervous system, mostly involuntary.
The somatic (motor) nervous system
carries signals to and from skeletal muscles and
mainly responds to external stimuli.
The autonomic nervous system
regulates the internal environment and
controls smooth and cardiac muscle and organs and glands of the digestive, cardiovascular, excretory, and endocrine systems.
The autonomic nervous system (ANS)
is composed of 3 divisions
The parasympathetic division
primes the body for activities that gain and conserve energy for the body. “D” divison = digestion, defecation and diuresis. a.k.a. “House-Keeper division” or “Rest and Digest” division
The sympathetic division
prepares the body for intense, energy-consuming activities. “E” = emergency, excitement, embarrassment. a.k.a. “Fight-or-Flight Division”
The enteric division
consists of networks of neurons in the digestive tract, pancreas, and gallbladder that control secretion and peristalsis.
The human brain is
more powerful than the most sophisticated computer and
composed of three main parts:
forebrain,
midbrain, and
The brainstem
- medulla oblongata
- controls breathing, HR, swallowing- pons
- bridge between forebrain and cerebellum
- controls breathing
- many important nerves originate here
- midbrain
- coordinates visual and auditory reflexes
- pons
The Cerebellum
= “little brain”
- coordinates movements initiated by cerebrum
The diencephalon
- Thalamus
- relay center for most senses
- deals with both emotions and most senses
- Hypothalamus
- controls pituitary and ANS
- therefore, controls much of homeostasis
The cerebrum is
part of the forebrain and
the largest and most complex part of the brain.
Most of the cerebrum’s integrative power resides in the cerebral cortex of the two cerebral hemispheres.
Plays a major role in memory, learning, and speech
Formulates complex behavioral responses
The cerebral cortex
is less than 5 mm thick and
accounts for 80% of the total gray of gray matter.
Specialized integrative regions of the cerebral cortex include
the somatosensory cortex - the main sensory receptive area for the sense of touch
centers for vision, hearing, taste, and smell ……(more about this later)
Association areas
make up most of the cerebrum and
are concerned with higher mental activities such as reasoning and language
lateralization
In a phenomenon known as lateralization, right and left cerebral hemispheres tend to specialize in different mental tasks. 95% of right-handed people have left-hemisphere dominance for language, 18.8% of left-handed people have right-hemisphere dominance for language function.
Frontal lobe
motor
Frontal association area of the brain helps plan movements.
It is also involved with personality, control of emotions and expression of emotional behavior.
Temporal lobe
Association centers for Hearing and Smell
Occiptal lobe
Association centers for Vision
Parietal Lobe
Association area for Touch
