Vertebrate Histology Lecture Exam II

What are the 3 functions of the nervous system?

1. Sensory

2. Integrative

3. Motor

Sensory Function

Nervous system senses stimuli within and external to the body

Integrative Function

Nervous system analyzes information, store some aspects, and makes decisions regarding it

Motor Function

Nervous system responds to stimuli by initiating muscular contractions and glandular secretions

What are the 2 major divisions of the nervous system?

Central and Peripheral

What does the CNS consist of?

Brain and spinal cord

What does the PNS do?

connects CNS to effectors

What is the PNS made of?

Nerves

Ganglion

Nerve cell bodies that cluster together

Nerves

nerve fibers wrapped in fibrous connective tissue

What does the input component of the PNS contain?

Afferent (sensory) neurons

What do afferent neurons do?

conduct nerve impulses from receptors to CNS

What does the output component of the PNS contain?

Efferent (motor) neurons

What are efferent neurons?

nerve cells that carry impulses from CNS to effectors

Effectors

muscles and glands

What 2 types of cells exist in nerve tissue?

Neuroglia and neurons

What do neuroglia do?

• provide support and protection

• undergo mitosis

Glioma

tumors that arise from neuroglia

What are 4 types of neuroglia in the CNS?

1. Astrocytes

2. Oligodendrocytes

3. Microglia

4. Ependymal Cells

What is the most abundant type of neuroglial cell?

Astrocyte

Functions of Astrocytes

• producing/absorbing neurotransmitters

• Maintaining potassium levels in CNS

• Help form blood brain barrier

• connect neurons and blood vessels

• providing sugar to neurons for ATP production

What is the importance of potassium in the CNS?

Aids in nerve impulses

What happens if neurons are damaged?

Astrocytes can form scar tissue, but can’t produce impulses

What do oligodendrocytes do?

produce myelin sheaths in CNS

What are microglia?

phagocytic cells derived from monocytes

What is the function of monocytes?

Protect the CNS by engulfing microbes and foreign debris

What are ependymal cells?

Cuboidal epithelial cells

Ependymal cell function:

• many are ciliated

• line ventricles within brain

• help produce CSF

What 2 types of neuroglia exist in the PNS?

1. Neurolemmocytes (Schwann Cells)

2. Satellite cells

What do neurolemmocytes do?

produce myelin sheaths around neurons in PNS

What do satellite cells do?

• provide support to neurons in PNS

  • aid in monitoring chemical environment around PNS neurons

What limited ability do neurons have?

self-repair and replacement

What are the 3 properties of neurons?

1. Excitability

2. Conductivity

3. Secretion

Excitability

ability to respond to stimuli by creating and conducting impulses

What ion movements do nerve impulses rely on?

Sodium and potassium ion movements across plasma membrane of a neuron

Conductivity

Ability to rapidly conduct impulses to other neurons or effectors

Secretion

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

What are the 3 parts of a neuron?

1. Cell body

2. Dendrites

3. Axons

Neuron cell body

contains organelles and cytoplasm

Dendrites

highly branched structures that emerge from cell body and receive impulses via neurotransmitters

Axons

long projection extending from cell body that carries impulses away from neuron

4 Parts of an Axon

1. Axon Hillock

2. Axoplasm

3. Axolemma

4. Axon terminals

Axon Hillock

site where axon attaches to cell body

Axoplasm

liquid portion of an axon

Axolemma

membrane that surrounds an axon

Axon terminals

• at tip of axon

• found at synapses

Synapse

points where neurons come together with other neurons or effectors

What do axon terminals store?

neurotransmitters in synaptic vesicles

Synaptic Cleft

The space between the axon terminal and the next cell

What are axons covered by in some neurons?

myelin sheaths

What are myelin sheaths?

A series of circular tissue layers around the axons of some neurons composed of lipids and proteins

What is the function of myelin sheaths?

to serve as an insulating layer

Neurilemma

The outer layer of a myelin sheath

What do myelin sheaths increase?

the speed of impulse conduction in the body

Nodes of Ranvier

the gaps in myelin sheaths

The amount of myelin _______ from birth to maturity

increases

Myelinated neurons are referred to as _____ _____

White matter

Unmyelinated sheaths are referred to as ____ _____

Gray matter

What 3 ways are neurons classified by structure?

1. Multipolar neurons

2. Bipolar neurons

3. Unipolar neurons

Multipolar neurons

• several dendrites and one axon

• common in brain and spinal cord

• most common neurons in body

Bipolar Neurons

• one dendrite and one axon

• found in the retina

Unipolar Neuron

• only one process extending from cell body

• dendrite at one end and axon in the other

What 3 ways are neurons classified by their function?

1. Afferent (sensory) neurons

2. Efferent (motor) neurons

3. Interneurons (association neurons)

Structural neuron classification is based on _______

how many processes extend from cell body

Functional neuron classification is based on _________

direction in which they transmit impulses

Interneurons (association neurons)

• between motor and sensory neurons

• carry signals through CNS

Cell regeneration in PNS

can only occur if neuron cell body is intact

Neurons in the CNS ____ regenerate

cannot

What are the 2 types of synapses?

1. Chemical synapses

2. Electrical synapses

Chemical Synapses

involve release of neurotransmitters that carry impulses from a neuron, across a synaptic cleft to another cell

Where are chemical synapses found?

1. between neurons

2. between neurons and skeletal muscle fibers

3. between neurons and glands

How are neurotransmitters classified?

excitatory or inhibitory

3 Specific Neurotransmitters

1. Acetylcholine

2. Norepinephrine

3. GABA

Acetylcholine

• excitatory

• stimulates muscle to contract

Norepinephrine

• excitatory

• stimulates responses in Autonomic Nervous System

GABA

• inhibitory

• minimizes neuronal activity and produces calming effect

What neurons are electrical synapses associated with?

cardiac and smooth muscle

How do ions move in electrical synapses?

directly between neurons and other cells

Neurotransmitters ____ required for electrical synapses

are not

Neurulation

development of the nervous system in a developing embryo

What are the 3 steps in neurulation?

1. Neural Plate formation

2. Neural Groove formation

3. Formation of forebrain, midbrain, and hindbrain

Neural Plate Formation

• occurs in week 3

• cells develop into neurons and most neuroglia

Neural Groove Formation

• neural fold develops around neural groove

• become cavities in brain and spinal cord that contain CSF

Forebrain

develops into cerebrum, thalamus, and hypothalamus

Midbrain

develops into part of brainstem

Hindbrain

develops into cerebellum and medulla oblongata

2 major connective tissue coverings around the brain

1. The skull

2. Cranial Meninges

Skull

composed of bone, protects brain

3 Cranial Meninges

1. Dura Mater

2. Arachnoid Layer

3. Pia Mater

Dura Mater

outer layer that forms protective bag around brain

What is the dura mater composed of?

dense irregular connective tissue

Epidural Space

space between skull and dura mater

What tissue does the epidural space contain?

adipose tissue

Arachnoid layer

middle layer of meninges

What tissues does the arachnoid layer contain?

• large supply of collagen and elastic fibers

• looks like a spider web

The arachnoid layer is ________

Avascular

Subdural Space

space between dura mater and arachnoid layer

What fluid fills the subdural space?

interstitial (tissue) fluid

Pia Mater

• innermost meninge

• transparent layer of connective tissue that adheres to and covers brain and spinal cord

The pia mater is ________

highly vascular