BSC 120 Lecture Notes - Lecture 48: Motor Neuron, Neuroglia, Sensory Neuron
29 Apr 2018
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Chapter 48 and 49 – The Nervous System
I. Nervous System
a. Neuron- basic unit of nerve cell
i. Nerve cells specialized for carrying chemical signals and electrical signals
from one part of the body to another
ii. If a neuron is destroyed, it is not replaced
iii. Glial cells support neurons and modify neuronal communication
1. Outnumber neurons 50:1
2. Divide and replace and provide nourishment for neurons (carbs
that it can metabolize)
3. Some keep brain from being infected and maintain cerebral fluid
4. Glial cell tumors are the most common tumors (no cure)
5. Types
a. Microglia – protect
b. Oligodendrocytes – axon myelination (CNS)
c. Schwann Cells – axon myelination (PNS)
d. Astrocytes – support, release neurotransmitters
iv. 3 types of neurons
1. Sensory neurons – sensory input
2. Interneurons – integrate info
3. Motor neurons – function in motor output
4. Effectors perform the body’s responses to motor output – muscles
or glands
b. Overview of Animal Nervous Systems
i. Nervous system forms a communication and coordination network
throughout an animal’s body
1. Receives info – input
2. Process info – integration
3. Send out info – output
ii. Cell body
1. Houses the nucleus and other organelles
2. Has mitochondria and golgi
3. Two types of extensions project from cell body:
a. Dendrites
i. Receive incoming messages from other cells
ii. Convey info toward cell body
1. Can only move in one direction
b. Axons
i. Transmit signals toward another neuron or toward
an effector (axon, muscle cell, or gland)
ii. Ends in a cluster of brances, each with a bulb-like
synaptic terminal that relays signals to another
neuron or an effector across a synapse
iii. Has adapted to have a mylon sheath – layers of
connective tissue that insulate the “wire”
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Chapter 48 and 49 – The Nervous System
1. Wraps. Around neuron (like insulation)
carries nerve impulses faster (myelin rich in
fat, appears glossy white)
2. Signal can pass quicker
3. Multiple sclerosis- results from a
dismantling of the myelin covering of CNS
axons by the body’s own immune system
a. New signals cannot be transmitted at
a rapid pace
b. Makes muscle movements difficult
c. Continues to get worse over time
c. Sending a signal through a neuron
i. A resting neuron has potential energy that can be put to work to send
nerve signals form one part of the body to another
1. This difference in charge (voltage) across the plasma membrane of
a resting neuron is the resting potential
2. Ex: Potassium/sodium pump
a. Neuron at rest has more sodium neurons outside than inside
ii. The action potential
1. A stimulus is any factor that causes a nerve signal to be generated
2. A stimulus of sufficient strength can trigger an action potential, a
nerve signal that carries information along a neuron
a. All or nothing
b. If there is enough stimulus then all action potentials are the
same strength
3. A nerve impulse travels along as an electrical current
4. Does this by ions moving in and out of the neuron through voltage-
gated channels
iii. Propagation of the signal
1. An action potential is a localized electrical event
2. To function as a nerve signal over distance, this local event must
be passed along the neuron
3. Action potential propagation is like a domino effect along a neuron
a. AKA it is progressive and self-sustained
4. Phases
a. Resting potential – unstimulated – polarized state – 70mV
i. 3 Na+ outside and 2K+ inside (Na+/K+ ion pumps)
ATP needed
b. Graded potential – local event – voltage gated channel
opens
i. Na+ moves in (to transmit has to reach a threshold)
c. Action potential – traveling long distance – depolarization
i. Na+ rushes in – signal passed along as a cascade =
30mV
d. Repolarization – K+ channels to the outside (ions opposite)
i. Voltage gated channel opens
find more resources at oneclass.com
find more resources at oneclass.com
