Nervous tissue

Question 1

What are the two classes of cells in nervous tissue?

Answer 1

Neurons and glia

Question 2

What is the CNS?

Answer 2

Central nervous system is contained within the spinal column and skull: 1. Brain 2. Spinal chord

Question 3

What is the PNS?

Answer 3

Peripheral nervous system is primarily outside of spinal columns and skull: 1. nerves 2. ganglia

Question 4

What is the difference between afferent and efferent?

Answer 4

Afferent = sensory = incoming – from receptor to CNS Efferent = motor = outgoing – from CNS to effector

Question 5

What is the difference between somatic and autonomic divisions?

Answer 5

Based on targets of efferent information and sources of afferent information: Somatic = part of the nervous system having to do with the body (soma = body) Autonomic = monitors and controls functions that are internal (i.e. blood pressure, heart rate, gut motility, oxygenation, etc)

Question 6

What do somatic efferent fibers do?

Answer 6

ALWAYS and ONLY innervate skeletal muscle (AKA: General Somatic Efferent)

Question 7

What do Autonomic efferent fibers do?

Answer 7

Innervate: Cardiac muscle, smooth muscle, glands, and fat NEVER innervate: skeletal muscle (AKA General Visceral Efferent)

Question 8

What do Somatic afferent fibers do?

Answer 8

Collect information regarding the body. Includes: - Pain - Temperature - Touch - Pressure - joint position - information from golgi tendon organs and muscle spindles Most of which we can be concious of and can pinpoint (AKA General Somatic Afferent)

Question 9

What do Autonomic afferent fibers do?

Answer 9

Collect information such as degree of stretch and chemical composition from internal organs and blood vessels (AKA General Visceral Afferent)

Question 10

What is the embryonic origin of the cells int he CNS?

Answer 10

Both neuronal and non-neuronal CNS cells are derived from the neural tube. - The neural tube originates from epithelial cells in the ectoderm.

Question 11

What characteristics do epithelial tissue and nervous tissue share?

Answer 11

Because nervous tissue originates from epithelial tissue in the neural tube, it has: - No connective tissue except that which surrounds the CNS and the blood vessels that penetrate the CNS - Entire CNS is surrounded by basal lamina (that began as basal lamina of neural tube) - Brain and spinal cord have fluid filled cavities lined by ependyma (epithelial cells)

Question 12

Describe the two sections shown

Answer 12

1. White matter: contains oligodendrocytes, nerve processes
2. Gray matter: Made up of dorsal and ventral horns; contain neuron cell bodies and microglial cells

Question 13

Where would you find spinal nerves?

Answer 13

They are formed where the dorsal and ventral roots meet.

• less than an inch long
• extend distally only to the point where the nerve divides into dorsal and ventral rami

Question 14

What type of nerve fibers exist in spinal nerves?

Answer 14

Spinal nerves are mixed nerves

• contain both afferent and efferent fibers
• also contain elements of both the somatic and autonomic systems

Question 15

How many spinal nerves are there in a human?

Answer 15

31

Question 16

What would result from cutting a dorsal root?

Answer 16

Dorsal roots are completely sensory

• cutting root results in loss of sensation, both somatic and visceral

Question 17

What is the dorsal root ganglion?

Answer 17

Near the distal end of the dorsal root, right where it exits an intervertebral foramen, is the DRG

• contains the cell bodies of the dorsal root neurons
• Each cell body has a peripheral process that receives information from receptors and a central process taht enters the spinal cord
• There are no synapses in the dorsal root ganglion

Question 18

What would result from cutting a ventral root?

Answer 18

Ventral roots are completely motor

• cutting this root results in paralysis
• both somatic and autonomic fibers are involved
• there are no ganglion along the ventral root; cell bodies are located in spinal cord

Question 19

What is the general principal of Autonomic Efferents? What makes them differnt from Somatic Efferents?

Answer 19

• All Autonomic pathways from CNS to target organ (heart, smooth muscle, glands) have TWO neurons (somatic have one)
• Preganglionic neuron = cell body in CNS
• Postganglionic neuron = cell body in ganglion
• Autonomic ganglia have synapses; somatic do not
• Autonomic ganglion = ALWAYS motor/efferent; Somatic = ALWAYS sensory/afferent

Question 20

Fill in the chart:

Answer 20

Question 21

What can be found in the gray matter of the spinal cord?

Answer 21

neuronal cell bodies and their dendrites, along with axons and central microglia

• synapses occur here

Question 22

What can be found in the white matter of the spinal cord?

Answer 22

• Myelinated and unmyelinated axons
• Oligodendrocytes

Question 23

Explain the connective tissue of the CNS

Answer 23

Three sequential connective tissue membranes, called the meninges, cover the brain and spinal cord:

• Dura mater = outermost layer
• arachnoid mater = layer beneath the dura
• pia mater = delicate layer resting directly on surface of brain and spinal cord

Question 24

What is a Nissl body?

Answer 24

Prominent in neuron cell bodies with toluidine blue stain, Nissl bodies are stacks of rER.

• They are so prominent b/c neurons are constantly making large amounts of proteins

Question 25

What is the embryonic origin of the PNS?

Answer 25

Both neurons and glia develop from the neural crest

Question 26

Describe the cell body of a neuron

Answer 26

large and euchromatic nucleus, prominent nucleolus, stacks of rER (Nissl bodies), visible in light microscope

Question 27

Describe the dendrites of a neuron

Answer 27

there are multiple per neuron attached to the cell body - they contain ribosomes

Question 28

Describe the axon of a neuron

Answer 28

- One per neuron - originating from the axon hillock - contains microtubules, neurofilaments for axoplasmic transport and mitochondria - generally surrounded by myelin for insulation of action potential

Question 29

Describe the terminals of neuron axons (nerve endings)

Answer 29

- nerve terminals contain neurotransmitters and form the synapses with other cells - terminals may be branched to form several synaptic endings attached to different postsynaptic cells --\> lesser branched or non-branched endings are often called boutons

Question 30

What is a neuromuscular junction?

Answer 30

- Elaborate, specialized synaptic endings of neurons on muscle cells - axons split into several synaptic endings - narrow intercellular gap (synaptic cleft) separates pre- and postsynaptic cells - presynaptic axon terminal filled with storage organelles called synaptic vesicles that contain neurotransmitters - synapses release vesicles/neurotransmitters by exocytossi into synaptic cleft and they diffuse to postsynaptic cell receptors

Question 31

What are sensory receptors?

Answer 31

Cells or complex aggregates of receptive and supportive cells

Question 32

What is a sensory unit?

Answer 32

Includes the sensory receptor plus all the cells in the pathway of information transfer up to the point o fthe initial synaptic contact within the CNS

Question 33

What are the connective tissues surrounding neurons?

Answer 33

Epineurium = dense irregular connective tissue surrounds a peripheral nerve and fills the spaces between nerve fascicles Perineurium = specialized connective tissue surrounding each nerve fascicle Endoneurium = includes loose connective tissue surrounding each individual nerve fiber; contains blood vessels

Question 34

What are exteroceptors?

Answer 34

Receptors that react to stimuli from the external environment i.e. temperature, toch, smell, sound, and vision

Question 35

What are Enteroceptors?

Answer 35

Receptors that react to stimuli from within the body i.e. degree of filling or stretch of the alimentary canal, bladder, and blood vessels

Question 36

What are proprioceptors?

Answer 36

Receptors that react to stimuli from within the body, provide sensation of body position and muscle tone and movement

Question 37

What are astrocytes (astroglia)?

Answer 37

1. Largest glia cells with many cytoplasmic processes; many cytoplasmic organelles such as intermediate filaments 2. many processes contact blood vessels and nearly continuously envelop the vessels with "astroglia feet," providing the basis of the blood-brain-barrier 3. Surround most neurons and provide structural support. - also provide key metabolic support for ionic environment and uptake of metabolic waste and toxic molecules

Question 38

What occurs when CNS tissue is damaged? (in terms of astrocytes)

Answer 38

A specialized form of astroglia appears (reactive or stellar astrocytes). - fill the space of killed neurons and eventually form the glia scar

Question 39

What are oligodendrocytes (oligodendroglia)?

Answer 39

1. Most numerous glial cell. Smaller than astrocytes with shorter, fewer processes. - nuclei and cytoplasm more condensed than astrocytes, contain ribosomes, mitochondria, microtubules 2. form myelin sheath for CNS - found mostly in white matter, but also abundant in gray

Question 40

Why do neurons need a myelin sheath?

Answer 40

Myelin acts as an electrical insulator - allows for faster action potential conduction than unmyelinated neurons

Question 41

What are the nodes of Ranvier?

Answer 41

Small gaps between adjacent myelin segments (between myelinating cells)

Question 42

What is myelin?

Answer 42

Almost pur plasma membrane, is very rich in lipid - due to high lipid content (which is extracted during conventional paraffin embedding), myelinated axons in paraffin sections are badly distorted by artifacts

Question 43

What are Schwann Cells?

Answer 43

The myelinating cells of the PNS 1. Main supporting cells of PNS 2. Even form coating around unmyelinated axons (the smallest axons)

Question 44

What are microglia?

Answer 44

Smallest glial cells with highly condensed nuclei and short, thorn-like projections - NOT derived from neuroepithelium - resident phagocytotic cells of the CNS - accumulate at sites of injury andphagocytose debris (called Gitter cells)

Question 45

What are ependymal cells?

Answer 45

Cuboidal/columnar cells with apical microvilli and, frequently, one or more cilia that line the central canal of the spinal cord and ventricles of the brain - basal lamina has been pushed far away - to the perimeter of the CNS - and so these cells are like the apical cells of very highly stratified epithelium - joined by modified junctional complexes (no zonulae occludentes); allows CSF to exchange "freely"

Question 46

What are satellite cells?

Answer 46

Originating from neural crest, satellite cells are flattened supporting cells covering peripheral ganglia - maintain the environment for the nerve cell bodies, analagous to schwann cells on axons