nervous system

as a whole, what does the nervous system control

all we do and all that we are

what’s makes up the CNS; another name for it

brain and spinal cord; also called tracts

what makes up the PNS

all nerves leaving the brain or spinal cord

the systems under PNS

somatic and autonomic nervous system

purpose of somatic nervous system

communicates voluntary (conscious) instructions to muscle

purpose of autonomic nervous system

communicates instructions to the viscera (involuntary subconscious actions)

purpose of autonomic and somatic working together

providing sensory, integrative, and motor functions

whats a neuron

structural and functional part of the nervous system that react to physical and chemical changes

how do neurons function

they transmit info through bioelectrical changes known as nerve impulses (action potential)

where is the impulse sent through an neuron

sent along nerve fibers (dendrites and axons)

what are nerves

bundles of fibers

what else does nervous tissue include

neuroglial cells (glial)

common features of a neuron

• cell body (soma)

• cytoplasm filled tubes that conduct impulses

• cell membrane separating the internal environment from the external environment

• cell organelles

• chromatophilic substance (nissl bodies) → similar to rough ER

• large nucleus with visible nucleolus

do mature neurons divide

no

what are the 2 different nerve fibers

dendrites and axons

what’s a dendrite

cell body will have many fibers

• short + highly branched

• main receptive surfaces

• conducts impulses into cell body

what’s an axon

cell body has one

• arise from “axonal hillock”

• begins as a single fiber, but will branch at end

• conducts impulses away from the cell body

• axon terminal ends at the synpatic knob

what are schwann cells

• sheaths around an axon composed of myelin

• membrane portion is called the neurilemma

• narrow gaps between schwann cells called nodes of ranvier

• fibers within the CNS that are myelinated form “white matter”

how do neurons differ from each other

size, shape, length, length of their axons/dendrites, and their function

how are neurons structurally classified

• bipolar

• unipolar

• multipolar

what’s a bipolar neuron

• only 2 nerve fibers, one arising from each end

• one acts as the axon and the other a dendrite

examples of where bipolar neurons are located

typically sensory neurons in the eyes, nose, and ear

what’s a unipolar neuron

• a single nerve fiber that extends from the body + branches off

• one end connects to a peripheral body part (dendrite) and the other to the brain or spinal cord (axon)

examples of where unipolar neurons are located

skin receptors, joints, muscles, and internal organs

what’s a multipolar neuron

many nerve fibers extend from the cell body, but only one acts as the axon

examples of where multipolar neurons are located

most lie in the brain or spinal cord

how are neurons functionally classified

• sensory

• interneuron

• motor neurons

what are sensory neurons

• afferent

• carries nerve impulses from the peripheral body (skin) INTO the brain or spinal cord

• most are unipolar

what are interneurons

• association

• lie WITHIN the brain or spinal cord and link to other neurons or transmit impulses from one part of the brain to another

• most are multipolar

what are motor neurons

• efferent

• carry impulses OUT OF the brain or spinal cord to effectors (muscles or organs)

• most are multipolar

what happens when neurons are deprived of oxygen?

they irreversibly change, with altered shapes and shrunken nuclei; this ischemic cell change eventually disintegrates the cells

how does oxygen deficiency in neurons occur

• lack of blood flow (ischemia)

• abnormally low blood oxygen levels (hypoxemia)

purpose of neuroglial cells

• fill space

• support neurons

• provide structural framework

• produce myelin

• carry on phagocytosis

what are microglial cells

• found throughout the CNS

• supports neurons

• phagocytize bacterial cells and other debris

what are oligodendrocytes

• found adjacent to nerve fibers

• forms the myelin within the CNS

what are astrocytes

• commonly found between neurons and blood vessels

• provide support, and helps to regulate nutrients

• constrict and dilate blood vessels

what are ependymal

• circulates cerebrospinal fluid (CSF)

• forms a barrier between the CSF and interstitial fluid

what are satellite

• provides structural, insulation, support, and nourishment

• cushions and protects the soma

what glial cells are with the CNS

• astrocytes

• ependymal

• oligodendrocytes

• microglial

what glial cells are with the PNS

• satellite

• schwann

what’s a nerve impulse? what does it consist of

a signal transmitted along a nerve fiber (axon). consists of a wave of electrical depolarization that reverses the potential difference across the nerve cell membrane

what are the steps involved in nerve impulse

1. resting potential

2. stimulation

3. threshold potential

4. depolarization

5. repolarization

6. refractory period

is the surface of a neuron charged?

the neuron membrane is electrically charged (polarized)

why does the polarization of the neuron occur? is there. aterm for it - if so, what?

due to unequal distribution of positive and negative ion concentrations which is known as potential difference

what’s the potential difference charged

-70mV

what do we find at resting potential

a greater concentration of K+ ions on the inside and Na+ on the outside [of the membrane']

where else are negative ions found? are they stuck there?

inside the membrane; due to being too large, they can’t cross the cell membrane

examples of large negative ions

phosphate (PO4^-3), sulfate (SO4^-2), and proteins

why is inside the neuron membrane negative

due to the large negative ions inside the resting neuron

what controls the distribution of ions on both sides of the membrane

• 1st facilitated diffusion (protein channels)

• 2nd active transport (sodium potassium pump)

how does the sodium potassium pump work?

ATP is used to move 3 Na+ ions out of the cell while pumping 2 K+ ions into the cell

what’s easier to pass through the cell membrane? K+ or Na+?

Potassium ions (K+)

are neurons excitable? what does this mean?

yes, neurons are excitable, meaning they can respond to stimuli and generate nerve impulses

what can change membrane permeability and how

environmental changes; opens the gated ion channels, causing the depolarization of the membrane

what does “potential change are graded” mean

degree of change in resting potential is directly proportional to the intensity of stimulation

what threshold potential

level of potential charge at which an action potential is triggered in a neuron

what’s action potential also known as

nerve impulse

what needs to trigger an action potential?

membrane potential must drop from -70mV to -55mV due to Na+ ions entering the cell

what’s subthreshold

a stimulus too small to create an action potential in a motor neuron

what’s threshold stimulus

a stimulus strong enough to create an action potential in a motor neuron

summary of potential change

changes that affect the resting potential

process of potential change

1. as the membrane resting potential decreases (from -70mV), the membrane depolarizes

2. the means stimulation has occured

3. changes in the resting potential of a membrane vary

4. the amount of change depends on the intensity

5. this additive phenomenon of intensity is called SUMMATION

during action potential, what occurs within the threshold potential?

permeability of the membrane suddenly changes, and voltage gated ion-channels begin to open

what aids the movement of positive ions into the cell?

concentration gradient

what is action potential? how long does this process take

when sodium ions diffuse inward to depolarize the membrane, as potassium diffuses out to repolarize the membrane.

the whole process takes only 1/1000 of a second

what works to make sure the original concentration of ions are kept during action potential

active transport

when action potential occurs in one region, what does it trigger?

causes a bioelectric current to flow to the adjacent downstream part of the membrane; this triggers a local current -creating wave of action potentials, which move down the fiber. the progression of action potentials creates a NERVE IMPULSE

as local currents progress, what now occurs? (repolarization)

the repolarized neuron has Na+ ions inside the K+ ions outside

when the Na+ ions are on the inside and K+ are on the outside, does it mean it’s now at resting potential

no

what needs to occur to re-establish resting potential? why does resting potetnial need to be reached

the sodium potassium pump must reorganize the proper ion distribution of Na+ on the outside and K+ inside; this is required before another action potential can be stimulated

review of events leading to conduction of a nerve impulsve

1. nerve cell membrane maintains resting potential (-70mV) by diffusion of Na+ and K+ down their concentration gradients as the cell pumps them up the gradients

2. neurons receive stimulation, causing local potentials, which may sum to reach threshold (-55mV)

3. sodium ions diffuse inward, depolarizing the membrane (+40mV)

4. potassium channels in the membrane open

5. potassium ions diffuse outward, repolarizing the membrane

6. action potentials occur sequentially along the length of the axon

what does an unmyelinated nerve do

conducts an impulse over its entire surface (grey matter)

how does a myelinated nerve behave comparing to an unmyelinated one

a myelinated nerve jumps from node to node because myelin prevents the conduction of the impulse

what’s saltatory

the impulse conduction of a myelinated nerve (jumping node-to-node) and moves many times faster than an unmyelinated nerve

what is the speed of the impulse conduction proportional to

diameter the of the fiber - greater the diameter, the faster the impulse. up to 120 mps

how fast can an impulse conduction go on an myelinated nerve

up to 0.5 mps