Human Anatomy Mike Aaron Ch 13

Functions of the Nervous System

sensory function, motor function, & integrative function

Sensory Function

the nervous system senses changes (stimuli) within the body and external to the body

Motor Function

the nervous system responds to stimuli by initiating muscular contractions and glandular secretions

Integrative Function

the nervous system analyzes sensory information, stores some aspects of the sensory info, and makes decisions regarding the sensory info.

2 Major Divisions of the Nervous System

the Central Nervous System (CNS) & the Peripheral Nervous System (PNS)

Central Nervous System (CNS)

consists of the brain and spinal cord ; analyzes sensory info, creates emotions, thoughts, and memories and stimulates muscle contraction and glandular secretion

Peripheral Nervous System (PNS)

connects the CNS to effectors (glands & muscles) of the body ; relays sensory info from the body to the CNS

The PNS is made up of…

Nerves

Nerves

bundles of nerve fibers wrapped in fibrous connective tissue

Ganglion

nerve cell bodies clustered together

2 components of PNS

Input and Output Components

Input Component of PNS

Sensory (Afferent) Neurons

Sensory (Afferent) Neurons

nerve cells that conduct nerve impulses from the receptors in the body to the CNS. These inform the CNS of stimuli in or around the body

Output Component of PNS

Motor (Efferent) Neurons

Motor (Efferent) Neurons

nerve cells that carry impulses from the CNS to the effectors of the body. This portion allows the brain to signal muscles and glands to respond to commands

2 Major Divisions of PNS

the Somatic Nervous System (SNS) & the Autonomic Nervous System (ANS)

Somatic Nervous System (SNS)

Contains Sensory Neurons that carry information from cutaneous and special sense receptors in the head, body wall, and limbs to the CNS ; Motor Neurons here carry impulses to skeletal muscles ; voluntary

Autonomic Nervous System (ANS)

Sensory Neurons here relay info from the internal organs to the CNS ; Motor Neurons here carry impulses from the CNS to cardiac & smooth muscles ; Involuntary

2 Branches of the Motor Portion of ANS

the Sympathetic Division & the Parasympathetic Division

2 types of cells in nerve tissue

Neuroglia & Neurons

Neuroglia

support & protect neurons ; can undergo mitosis to multiply in number

Gliomas

tumors that arise from neuroglia

Types of Neuroglia in CNS

Astrocytes, Oligodendrocytes, Microglia, & Ependymal Cells

Astrocytes

most abundant ; many functions

Oligodendrocytes

produce myelin sheath in CNS

Microglia

phagocytic cells derived from monocytes (specialized leukocytes) ; aid in immune function by engulfing microbes and foreign debris

Ependymal Cells

Cuboidal Epithelium ; ciliated ; line ventricles in the brain ; produce Cerebrospinal Fluid

Types of Neuroglia in PNS

Neurolemmocytes (Schwann Cells) & Satellite Cells

Neurolemmocytes (Schwann Cells)

produce myelin sheath around neurons in PNS

Satellite Cells

provide support to neurons in PNS & monitor chemical environment around neurons

Neurons

limited ability to repair themselves

Properties of Neurons

Excitability, Conductivity, & Secretion

Excitability

the ability to respond to stimuli by creating and conducting impulses

Conductivity

the ability to conduct impulses rapidly to other neurons or to effectors

Secretion

neurons secrete neurotransmitters when the impulse reaches the end of the cell itself

Parts of a Neuron

Cell Body, Dendrites, & Axon

Cell Body

contains the organelles and cytoplasm of the neuron

Dendrites

highly branched structures that emerge from the cell body ; receive impulses from the axons of other neurons and conduct impulses to the cell body

Axon

long projection extending from the cell body ; carries impulses away from the cell body

Parts of an Axon

Axon Hillock, Axoplasm, Axolemma, Axon Terminals, Myelin Sheath (in some cases)

Axon Hillock

site where an axon attaches to the cell body

Axoplasm

liquid portion of an axon

Axolemma

membrane that surrounds an axon

Axon Terminals

at the tip of the axon ; found at Synapses

Synapses

points where neurons com together with other neurons or effectors

Synaptic Cleft

space between the axon terminal and the next cell

Synaptic Vesicles

special bags where axons store neurotransmitters

Myelin Sheath

composed of lipids and proteins ; insulating layer ; outer layer of tissue is called Neurilemma

Nodes of Ranvier

gaps in Myelin Sheath

White Matter

neurons covered in a Myelin Sheath

Gray Matter

unmyelinated neurons

Multiple Sclerosis (MS)

destruction of myelin sheath in the CNS caused by plaques (scars) ; characterized by abnormal sensations, muscle weakness, and decreased motor function

Tay-Sachs Disease

excess myelin accumulates around the axon ; causes short circuit of nerves leading to blindness, loss of balance, and dementia

Structural Classification of Neurons

Multipolar, Bipolar, Unipolar

Multipolar Neuron

has several dendrites and one axon ; most common in brain & spinal cord and human body

Bipolar Neuron

one dendrite and one axon extending from the cell body ; found in retina of the eye

Unipolar Neuron

have only one process extending from the cell body ; dendrite located at one end and the axon at the other end

Functional Classification of Neurons

Sensory (Afferent), Motor (Efferent), Interneurons (Association)

Interneurons (Association Neurons)

lie between motor and sensory neurons ; Carry signals to CNS where integration occurs

Presynaptic Cell vs Postsynaptic Cell

before synapses vs after synapses

Types of Synapses

Chemical & Electrical

Chemical Synapses

release of neurotransmitters that carry impulses from a neuron, across a synaptic cleft to another cell ; found between neurons, between neurons & skeletal muscle fibers, and between neurons & glands

Neurotransmitter Classifications

Excitatory or Inhibitory

Specific Neurotransmitters

Acetylcholine- excitatory; stimulates muscle contraction

Norepinephrine- excitatory; stimulates responses in Autonomic Nervous System

GABA-inhibitory; minimizes neuronal activity (calming effect)

Electrical Synapses

associated with neurons that stimulate cardiac and smooth muscle ; ions are free to move directly between neurons and other cells

Neural Circuits

pathways that illustrate the movement of impulses between interconnected neurons

Diverging Circuits

one axon (nerve fiber) branches and forms synapses with several post synaptic cells ; skeletal muscle tissue

Converging Circuits

impulses from several neurons are channeled into one neuron ; human respiration

Reverberating Circuits

neurons stimulate each other in a linear fashion one after the other

Parallel Circuits

a neuron diverges to stimulate parallel chains of neurons that reconverts at an output neuron

Neurulation

development of the nervous system in a developing embryo

Steps of development of the Nervous System

1. Neural Plate Formation

2. Neural Groove Formation

3. 3 Bulges: Forebrain, Midbrain, Hindbrain

Neural Plate Formation

occurs in week 3 of development ; cells here develop into neurons and most neuroglia

Neural Groove Formation

occurs as development continues ; Neural Fold develops around neural groove ; becomes cavities in brain and spinal cord that carry cerebrospinal fluid

Forebrain

develops into the cerebrum, thalamus, and hypothalamus

Midbrain

develops into part of the brainstem

Hindbrain

develops into cerebellum and medulla oblongata

Spina Bifida

vertebrae fail to unite to form a covering around the spinal cord ; Spina Bifida Cystica- a sac protrudes from the spine

Microcephaly

abnormally small brain caused by failure of neural tube to develop properly