Seeley's A&P 9th ed. Chapter 8 - Nervous System

Central Nervous System (CNS)

-consists of the brain and the spinal cord
- Processing and integrating information, initiates responses, mental activity

Peripheral Nervous System (PNS)

- consists of all the nervous tissue outside the CNS
- Nerves and Ganglia

Sensory Division of the PNS

- transmits the action potentials TO the CNS
- transmits information from the periphery

Motor Division of the PNS

- carries action potentials AWAY from the CNS
- transmit information to the periphery

MOTOR Division divided into:

Somatic and Autonomic Systems

The Somatic MOTOR Nervous System

- innervates skeletal muscle and is mostly under voluntary control

The Autonomic Nervous System

- innervates cardiac muscles, smooth muscle, and glands and is mostly under involuntary control.

The Autonomic Nervous is divided into:

sympathetic and parasympathetic divisions.

Sympathetic Divisions

- prepares a person for action by increasing heart rate, blood pressure, respiration and release of glucose for energy.
- "Fight and Flight"

Parasympathetic divisions.

- involved in involuntary activities at rest, such as the digestion of food, defecation, and urination.
- "Rest and Digest"
- Calming down

Cells of the Nervous System

Neurons and Glial Cells/Neuroglia

Neurons

receive stimuli and conduct action potentials.
transmit signals to other neurons or effector organs

An Effector

- is any part of the body that produces the response.
- examples of effectors: a muscle contracting to move the arm.
a muscle squeezing saliva from the salivary gland.

Glial Cells/ Neuroglia

- support cells of the of the nervous system
- nutrition
- insulation
- help with signal transmission in the Nervous System

Types of Neuroglia

- Astrocytes, ependymal cells, microglia, oligodendrocytes, and Schwann cells

Astrocytes

-star-shaped
-form blood-brain barrier
-most abundant
-for support
-regular ions

Microglial cells

-CNS Immunity
-defend
-help remove bacteria and cell debris from CNS

Ependymal Cells

-produce and circulate Cerebrospinal fluid (CSF)
-line cavities

Oligodendrocytes

-wrap and insulate
-produce/ form MYELIN sheath in CNS

Schwann cells

-insulate
-produce/help form MYELIN sheath in PNS

3 Parts of Neuron:

1. a cell body,
2. Two types of processes called: a. dendrites
b. axons

Cell Body of a Neuron

- contains single nucleus
- nucleus-containing central part of a neuron exclusive of its axons and dendrites that is the major structural element of the gray matter of the brain and spinal cord, the ganglia, and the retina

Cell Body of a Neuron

— also called perikaryon, soma.

The cell body (soma)

- the factory of the neuron. It produces all the proteins for the dendrites, axons and synaptic terminals and contains specialized organelles such as the mitochondria, Golgi apparatus, endoplasmic reticulum, secretory granules, ribosomes and polysomes to provide energy and make the parts, as well as a production line to assemble the parts into completed products.

Nissl Bodies / Rough Endoplasmic Reticulum

- has groups of ribosomes used for protein synthesis.
- dust like; to create the proteins.

Proteins produced in the Endoplasmic Reticulum

Neurotransmitters:
Acetylcholine
Dopamine
Serotonin
Norepinephrine
Nitric Oxide/Gases

Dendrites

- a short branched extension of a nerve cell, along which impulses received FROM other cells at synapses are transmitted TO the cell body.

Axon

- transmit electrical impulses AWAY from the cell body.

Axon

- the long threadlike part of a nerve cell along which impulses are conducted from the cell body to other cells.
- main conducting unit of the neuron, capable of conveying electrical signals along distances that range from as short as 0.1 mm to as long as 2 mm

Components of An Axon

Axon Hillock, Schwann cells, Myelin sheath, Node of Ranvier, Terminal Boutons(presynaptic terminals) and Collateral Axon(branch)

The Axon Hillock

- is where the axon is joined to the cell. It is from here that the electrical firing known as an action potential usually occurs.

Schwann Cells

- a myelin-secreting glial cell that spirally wraps around an axon of the peripheral nervous system to form the myelin sheath.

Myelin sheath

- insulating covering that surrounds an axon with multiple spiral layers of myelin, that is discontinuous at the nodes of Ranvier, and that increases the speed at which a nerve impulse can travel along an axon.

Node of Ranvier

- a small gap in the myelin sheath of a nerve, between adjacent Schwann cells.; approximately 1 micrometer wide.
- These gaps form on axons between the myelin sheath.

The nodes of Ranvier

They allow action potentials to pick up speed so they can propagate down the axon and reach the target cell or tissue.

Terminal Boutons (presynaptic terminals)

Axon terminals (also called synaptic boutons) are distal terminations of the branches of an axon.

Terminal Boutons

- club-shaped endings by which axons make synaptic contacts with other nerve cells or with effector cells (muscle or gland cells)

Saltatory conduction.

The rapid conduction of action potentials from one node to another is known as

Node of Ranvier

Myelin sheaths are comprised mostly of fat cells. Fat is a good insulator and does not allow for quick propagation of electrical signals through action potentials. The_______________ are free of myelin sheath cells.. They allow action potentials to pick up speed so they can propagate down the axon and reach the target cell or tissue.

Nucleus

- source of information for gene expression.
- contains the genes

Types of Neuron by Structure:

Multipolar, Bipolar and Pseudo-Unipolar Neurons

Multipolar Neuron

- 90% of Neurons are _________________
- has three or more processes sticking out from the SOMA(Body) including the Axons and a bunch of Dendrites.

Bipolar Neuron

- rarely found
- example: In the RETINA of the eye.
- it has 2 processes: Axon and a single Dendrite which are extending from opposite side of the body

Pseudo-Unipolar Neuron

- one process
- found mostly in Sensory receptors
- No Dendrite

Sensory Neuron and Motor Neuron

Types or Classification of Neurons by Function:

Sensory Neuron

- carrying / transmits information TO the CNS FROM the Body
- pick-up messages
-Transmit impulses from sensory receptors toward the CNS
(Sensory Receptors -Skin or internal organ)
-usually UNIPOLAR

Sensory Neuron or

Afferent Neuron

Motor Neuron

- sending information TO the body FROM the CNS
- transmit impulses AWAY from the CNS to the rest of the body/ OUT
- Glands and muscles
- ususally MULTIPOLAR

Motor Neuron or

Efferent Neuron

Interneuron or

Association Neuron

Interneuron

transmit impulses between sensory and motor neuron
-MULTIPOLAR

Process

projecting part from an organic part of a structure.
example: axon and dendrite of the Neuron.

Nervous Tissue

consists of White Matter and Gray matter.

Gray Matter

forms the cortex and nuclei in the brain and ganglia in the PNS.

White Matter

forms nerve tracts in the CNS and nerves in the PNS

Gray Matter parts

Posterior (Dorsal Horn)
Lateral Horn
Anterior Horn (Ventral Horn)

White Matter parts

Dorsal Column (Posterior)
Lateral Column
Ventral Column (Anterior)

Dorsal Horn (Posterior) of the Gray matter

Sensory Neuron - towards(IN) the dorsal horn

Ventral Horn (Anterior)of the Gray Matter

Somatic Motor Neuron - (Out) from the Ventral Horn

Lateral Horn of the Gray Matter

- (OUT) Autonomic neuron

Interneuron or Association Neuron

- receive impulses from the sensory neurons. They interpret the information received from other neurons and relay impulses to motor neurons for an appropriate response. This function of the ____________________ is called integration.

Action Potential

- occurs when the charge across the cell membrane is briefly reversed
- Chemically-gated and voltage-gated ion channels generate the _____________

Action Potential

- the rapid depolarization and repolarization of the cell membrane

All or none

- action potential occur in _________________fashion.
- if threshold is reached, an action potential occurs.
- if threshold not reached, no action potential occurs.

Saltatory conduction

- Type of action potential conduction wherein action potential "jump" from one of Ranvier to the next along the length of the axon.

Muscle Contraction

-in a muscle fiber, action potential results in ______________

Resting membrane potential

- results from the charge difference across the membrane of cell
- i.e. a cell that has not been stimulated to produce an action potential
- (-) 70 mV
- is set by leak ion channels and the Sodium-Potassium pump (Na+-K+)

Resting membrane potential

- Na+ channels and most but not all, K+ channels are closed.
- The outside of the cell membrane is positively charged compared to the inside.

Depolarization

- Na+ channels are open.
-K+ channels begin to open.
- inward movement of the Na+ makes the inside of the membrane positive.

Repolarization

- Na+ channels close
- additional K+ channel open.
- Na+ movement into the cell stops
- K+ movement out of the cell increases, causing ______________.

Polarize

- to create a difference in potential (charges) between two points, as between the inside and outside of cell membrane.

Depolarize

- decrease in the difference in potential (charge) between two points, as between the inside and outside of a cell membrane.

Repolarize

- the change back to the resting membrane potential.

Threshold value

- if the depolarization is large enough, Na+ enters the cell so that the local potential reaches a ______________

Hyperpolarization

- at the end of repolarization, the charge on the cell membrane briefly becomes more negative than the resting membrane potential.; this condition is called _________________.

Oscilloscope

- measuring tool for measuring resting membrane potential.

1. Na+-K+ Pump
2. K+ Leak Channel
3. Voltage-gated Na+ channel(-50mV)
4.Voltage-gated K+ Channel(+ 20mV)

4 Protein Channels

Ligand-gated channels

- open when a neurotransmitter latches onto its receptors

Voltage-gated channels

- opened by a change in membrane potential.

Synapse

- is a point of contact between two neurons or between a neuron and another cell, such as muscle or gland cell.

Neurotransmitter

- an action potential arriving at the synapse causes the release of a ____________ from the presynaptic terminal, which diffuses across the synaptic cleft and binds to the receptors of the postsynaptic membrane.

Spinal cord

- extends from the foramen magnum to the second lumbar vertebra.
-has a central gray part organized into horns and a peripheral white part forming the nerve tracts.

Spinal Nerves

exit the vertebral column at the cervical, thoracic, lumbar and sacral regions.

Ganglia

Nervous tissue
- a bundle of cell bodies in the PNS

Nerve

Nervous tissue
- a bundle of axons in the PNS

Nucleus

Nervous tissue
- a bundle of cell bodies in the CNS

Tract

Nervous tissue
- a bundle of axons in the CNS

Brainstem

- Portion of the brain consisting of the midbrain, pons, and medulla oblongata
- contains several nuclei

Forebrain

- Thalamus
- Hypothalamus
- Cerebrum

Thalamus

Function:
- Relay Center

Hypothalamus

Function::
- Control Body Temperature

Cerebrum

Function:
- associated with higher brain function such as thought and action.

Forebrain

- is the largest part of the brain, most of which is cerebrum. - The thalamus functions to relay sensory information to the cerebral cortex and the hypothalamus, regulating visceral functions including temperature, reproductive functions, eating, sleeping and the display of emotion

Midbrain

- Cerebral Peduncle
- Corpora Quadrigemina

Cerebral Peduncle

Function:
-Relay center

Corpora Quadrigemina

Function:
- analyzing reflexes for vision and hearing

Midbrain

- Superior end of the brainstem
- involved in hearing and in visual reflexes.

Hindbrain

- Pons
- Medulla
- Cerebellum

Pons

Function:
- Relay center
- Increase and decrease respiratory rate

Medulla

Function:
- controls heart beat and blood pressure
- involved in vital body functions