Chapter 11 Mastering A And P

axon

brain and spinal cord

Touch stimulation of this sensory receptor will open the mechanically gated ion channels, but action potentials are still not initiated because propagation of an action potential requires the opening of voltage-gated Na+ channels Propagation (spreading) of an action potential from the cell body to the axon hillock and eventually the axon terminals (synaptic knobs) requires the sequential opening of mechanically and voltage-gated ion channels. When the sequence is interrupted, the message cannot spread to the sensory regions of the central nervous system, causing numbness.

motor fibers that conduct nerve impulses from the CNS to smooth muscle, cardiac muscle, and glands

found in the retina of the eye

True

the somatic nervous system The somatic nervous system is composed of somatic motor nerve fibers that conduct impulses from the central nervous system to skeletal muscles. It is often referred to as the voluntary nervous system because it allows us to consciously control our skeletal muscles.

oligodendrocytes

analyzes sensory information, stores information, makes decisions

They are mitotic.

A neuron can have only one axon, but the axon may have occasional branches along its length this is true; a neuron can have only one axon, but the axon may have occasional branches along its length.

Most association neurons are confined within the peripheral nervous system (PNS) Most association neurons are confined within the CNS (not PNS).

central nervous system The central nervous system, which consists of the brain and spinal cord, is the integrating and control center of the nervous system. It interprets sensory input and dictates motor output based on reflexes, current conditions, and past experience.

the direction in which the nerve impulse travels relative to the central nervous system Functional classification groups neurons according to the direction in which the nerve impulse travels relative to the central nervous system. Based on this criterion, there are sensory neurons, motor neurons, and interneurons.

oligodendrocytes Oligodendrocytes wrap their processes around the thicker axons in the CNS, producing an insulating covering called a myelin sheath that increases the transmission speed of nerve impulses.

degree of myelination of the axon the rate of impulse propagation depends largely on two factors, degree of myelination and axon diameter. The presence of a myelin sheath dramatically increases the rate of impulse (action potential) propagation. Heavily myelinated axons propagate impulses faster than lightly myelinated axons. Also, larger (thicker) axons conduct impulses faster than smaller (thinner) axons.

the neuron cannot respond to another stimulus no matter how strong

The interior of the becomes less negative due to an influx of sodium ions

The specific period during which potassium ions diffuse out of the neuron due to a change in membrane permeability

Also known as a nerve impulse

an exceptionally strong stimulus that can trigger a response

ependymal cells line central cavities of the CNS. Much as the cilia of respiratory epithelium moves mucous along the surface of the tissue layer, the cilia of ependymal cells help circulate the cerebrospinal fluid that nourishes and cushions the brain and spinal cord.

sensory Input(receptors), Integration(control center), Motor Output(effector

Brain and spinal cord. Integration center for sensory input, dictates motor output

Nerves outside CNS. Divided into sensory (afferent) and motor (efferent) divisions

Somatic Sensor Fibers: Impulses from skin/superficial organs to CNS Visceral Sensory Fibers: impulses from deep organs (i.e. heart) to CNS

Somatic Nervous System: Voluntary muscle control (skeletal muscle) Auto nomic NS : Involuntary, S ympathetic & P arasympathetic subdivision

Neuron: nerve cells, do not divide. Neuroglia: support and protect neurons, can divide

CNS Astrocytes - Transport material between blood, neurons. Maintains homeostasis Microglial Cells - Phagocytosis of dead cells, bacteria Ependymal Cells - Line ventricles of the brain Oligodendrocytes - Wrap axons and secrete myelin, action potential travels faste

PNA: Sa tellite Cells - as astrocytes Schwann Cells - as Oligodendrocytes

Neurons are large, highly specialized cells that transmit electric impulses (action potentials). They are amito tic and have extreme longevity (100 yrs or more)

ring impulses into the cell body

Biosynthetic center and receptive region, contains organelles

Sends impulse to target via neurotransmitters released into synapse

Cell bodies, dendrites, axon terminals. Site of all synapses

Axons connecting different parts of gray matter to each other

Afferent Route, Unipolar, Bipolar

Efferent Route, Multipolar

CNS and multipolar

3 or more processes and Within CNS, Motor neurons

1 Axon and 1 Dendrite processs and Special sensory neurons

Divides T-like, 2 Axons and Tactile sensory neurons

Narrow synaptic cleft, neurotransmitter molecules are released from vesicles in presynaptic neuron axon terminals, bind dendrites of postsynaptic neuron

Capable of being innervated and transmitting and action potential

Membrane potential typically - 70 mV inside cell. ECF has higher concentration of sodium. ICF has higher concentration of potassium

Ligand: Chemical binding opens channel. Binding can be intracellular or extracellular Voltage: Opens when a certain electrical charge is reached Mechanically Gated: Physically moved to open

"All or none" phenomena, in order for an action potential to be produced neuron must depolarize by a speci fic amount, i.e. reach the threshold number

The axon hillock

Sodium and potassium. During repolarization sodium channels close, voltage - gated potassium channels open. Higher potassium concentration inside cell causes rapid diffusion out of cell to restore resting membrane potential. Sodium - potassium pumps restore original concentrations

Sodium influx causes local depolarization away from AP origin. Repolarization wave follows behind, resetting axon. This is continuous conduction. In Saltatory conduction AP jumps between nodes of Ranvier in myelinated axon. Much more rapid signaling

Axon terminals (presynaptic), Synaptic cleft, Motor end plate (postsynaptic)

AP opens voltage - gated calcium channels on terminal, Vesicles of Ach move down and fuse with membrane. Exocytosis releases Ach into synaptic cleft

Ach binds ligand - gated channels on motor end plate, opens them. Sodium ente rs and depolarizes membrane (brings membrane potential closer to 0). Depolarization wave propagates to t - tubules, calcium released from sarcoplasmic reticulum actin, myosin heads hydrolyze ATP, power stroke contracts muscle by moving thin filaments together

Acetyl choline. Excitatory effect, broken down by Acetylcholinesterase

Excitatory: depolarize postsynaptic membrane (move vol tage towards 0) Inhibitory: hyperpolarization of postsynaptic membrane (move voltage away from 0)

Continuous: Action potential propagates along axon from one region to adjoining areas Saltataory: Action potential jumps between nodes of Ranvier on myelinated axon