Functional Organization Of Nervous Tissue

Functions of the Nervous System

Maintaining homeostasis

Receiving sensory input

Integrating information

Controlling muscles and glands

Establishing and maintaining mental activity

Nervous System Organization

Central Nervous System (CNS)

Peripheral Nervous System (PNS)

Functional Organization of the Nervous System

Sensory (Input)

Motor(Output)

Motor Nervous System

Initiates and transmits information from the CNS to effectors

Somatic Motor

Motor output that is consciously or voluntarily controlled

Ex. Effector is skeletal muscle

Autonomic Motor

Motor output that is not consciously or is involuntarily controlled

Ex. Effectors are cardiac muscle, smooth muscle, and glands

Sensory Nervous System

Detects stimuli we consciously perceive

Somatic Sensory

Sensory input that is consciously perceived from receptors

Ex. Ears, Eyes, Skin

Visceral Sensory

Sensory input that is not consciously perceived from receptors of blood vessels and internal organs

Ex. Heart

Sensory

Afferent- Transmits action potentials from receptors toward the CNS.

Sensory Receptors

Sensory nerve endings that respond to stimuli

Motor

Efferent- Transmits action potentials from CNS to effectors.

SAME

Sensory (afferent)

Motor (efferent)

Somatic

Autonomic

Divisions of the Nervous System

Somatic Nervous System

From CNS to skeleton muscles. (Voluntary)

Autonomic Nervous System (ANS)

From CN to smooth muscle, cardiac muscle and certain glands

Autonomic Nervous System (ANS) Divisions

Sympathetic

Parasympathetic

Sympathetic (ANS)

Prepares body for physical activity (Fight or Flight)

Parasympathetic (ANS)

Regulates resting such as digesting food or emptying of the urinary bladder

Enteric (ANS)

Plexuses within the wall of the digestive tract (Gut Function)

Glial Cells of the CNS

Astrocytes
Oligodendrocytes
Microglia
Ependymal cells

Astrocytes

Blood brain barrier (CNS)

Oligodendrocytes

Form myelin sheath in CNS

Microglia

Phagocytic cells that ingest and break down waste products and pathogens in the CNS

Ependymal cells

Produce and circulate cerebrospinal fluid (CSF)

Glial Cells of the PNS

Schwann cells

Satellite cells

Schwann cells

Produce myelin in PNS

Satellite Cells

Surround neuron cell bodies in PNS

Myelinated Axons

Axons covered with myelin sheaths

Organization Of Nervous Tissue

Gray matter

White matter

Gray Matter

Unmyelinated axons

Cell bodies

Dendrites

Integrative functions

The cortex of the brain

White Matter

Myelinated axons

Propagate action potentials

Cluster of neuron cell bodies in the PNS

ganglia

Bundles of axons with CT sheaths in PNS

Nerves

Clusters of neuron cell bodies in CNS

Nuclei

Tracts

Bundles of myelinated axons in CNS

Sodium-Potassium Pump

Sodium is pumped outside the cell but wants to come in.

Potassium is pumped inside the cell and wants to go out.

Ligand-gated ion channel

Open or close in response to ligand such as neurotransmitter or hormone binding to receptor protein

Voltage-gated ion channel

Open or close in response to voltage changes

Other gated ion channels

Touch receptors: respond to mechanical stimulation of the skin

Temperature receptors: respond to temperature changes in the skin

Establishing the Resting Membrane Potential

Higher potassium inside

Higher sodium outside

Proteins stuck inside

Depolarization

Inside of cell becomes more positive

Hyperpolarization

Inside of cell becomes more negative

Two major ways to hyperpolarize

Potassium Ions- Making cell more negative (Most common)

Chloride Ions- Ligand- gated chloride channels causes chloride to enter cell adding negative charges hyperpolarizes the cell

Graded Potential

A shift in the electrical charge in a tiny localized area of a neuron

Action Potential- How neurons communicate

Graded potentials summate reaching threshold

All or none principle

No matter how strong the stimulus

As long as it is greater than threshold an action potential will occur

Depolarization

Sodium channels open

Incoming Sodium makes the inside of membrane more positive

As voltage changes more and more voltage-gated sodium channels open

Repolarization

As the membrane potential reaches its maximum depolarization voltage-gated sodium channels close and potassium open

Action Potential Frequency

Number of action potentials produced per unit of time to a stimulus

Subthreshold Stimulus

Stimulus not strong enough, so no contractions seen

Threshold Stimulus

Graded potential initiates an action potential

Submaximal Stimulus

Between threshold and maximal stimulus strength

Maximal Stimulus

Strong enough to produce a maximum frequency of action potentials

Supramaximal Stimulus

Any stimulus greater than maximal stimulus

Chemical Synapse Components

Presynaptic terminal

Synaptic cleft

Postsynaptic membrane

Receptors

Chemical Synapse Steps

1. Action potentials arriving at the presynaptic terminal

2. Voltage-gated Calcium channels open

3. Calcium enter cells causing synaptic vesicles to release neurotransmitter molecules

4. Neurotransmitter diffuse across the synaptic cleft

5. Neurotransmitter bind receptors in postsynaptic cell

6. Binding of neurotransmitter to ligand-gated sodium channels causes sodium to enter postsynaptic cell

7. If the resulting depolarization graded potential reaches threshold an action potential is produced

8. Neurotransmitter is cleared

(Potassium or Chloride would hyperpolarize)

Removal of Neurotransmitter from Synaptic Cleft

1. Enzymes can break down the neurotransmitter.

2. Neurotransmitter can be taken up presynaptic terminal and recycled

3. Neurotransmitter can diffuse away

Two Types Of Summation

Temporal

Spatial