Chapter 13 (lectures)

1. Sends sensory info to CNS

2. Send motor information to periphery

Two main functions of the PNS

1. Afferent fibers (periphery to CNS)

2. Efferent fibers (CNS to periphery)

Two types of fibers in PNS

Sensory receptor

Responds to changes in the environment

stimulus

Change in the environment

Sensation

The brain becomes aware of the stimulus

Perception

interpretation of the meaning of a stimulus

1. type of stimulus

2. Where they are located in the body

3. their structural complexity

How can receptors be classified? [3]

1. Mechanoreceptors

2. Thermoreceptors

3. Photoreceptors

4. Chemoreceptors

5. Nociceptors

Five classifications of stimulus by type:

Mechanoreceptors

Receptors that sense some sort of mechanical force happening to tissue

Thermoreceptors

Receptors that sense change in temperature

Photoreceptors

Receptors that sense light (mostly in eye)

Chemoreceptors

Receptors that respond to chemicals in solution (taste, smell, responding to different molecules in food). Can also respond to chemical changes in blood and interstitial fluid

Nociceptors

Receptors that respond to potentially dangerous stimuli, resulting in pain

1. Exteroceptors

2. Interceptors

3. Proprioceptors

Three classifications of receptors by location in the body

Exteroceptors

Receptors that are sensitive to stimuli that act outside the body (or near the body surface) from outside environment)

Interceptors (also called visceroceptors)

Receptors that respond and monitor stimuli within the body (ex: BP, HR, bladder)

Proprioceptors

Receptors that respond to internal stimuli. Are located in skeletal muscles, tendons, joint capsules, and ligaments. Constantly monitoring the position of the body and awareness of where it is in space.

1. General receptors (nonencapsulated)

2. Encapsulated receptors

Two classifications of receptors by their structure

Nonencapsulated receptors

Free nerve endings in tissue

Encapsulated receptors

Sensory neurons enclosed in a connective tissue capsule

1. Receptor level

2. Circuit level

3. Perceptual level

Three levels of processing (receptor stimulation)

Something happens in the environment that causes receptor to become stimulated/excited (i.e., receptors in muscle, in joints, or in free nerve endings in the skin). end result of simulation is always an action potential.

What happens at receptor level of stimulation?

The impulse is delivered to the appropriate region of the cerebral cortex. The region depends on where the stimulus was. Each stimulus is directed to different portions of the brain, depending where is came from. Processing to make sure signal is sent to right part of the cortex.

What happens at circuit level of stimulation?

Information is interpreted in the cerebral cortex. Since all neurons carry action potentials, it is interpreted differently depending where it came from. No matter how a receptor is activated, the interpretation will be the same. Signal takes on meaning in the cortex.

What happens at perceptual level of stimulation?

Pain

a warning signal from the body that something is not right

Extreme temperature,

extreme pressure,

chemical released from injured tissues.

How are pain receptors activated?[3]

Chemicals that act on small diameter nerve fibers.

1. Histamine

2. Potassium

3. ATP

4. acids

5. Bradykinins

What chemicals are released from injured tissues?

Neurotransmitters Glutamate and substance P. They activate secondary neurons ad trigger pain in the brain.

What is released as a result of pain receptors being activated? [2]

Visceral/referred pain

Happens because visceral pain travels in same pathways as somatic pain pathways. Sensory info from a visceral organ and an appendage travels along the same pathway, triggering pain in an appendage instead o the affected organ.

Nerve

Comprised of hundreds of neurons. Most are mixed (sensory and motor)

To convey motor information to the periphery

Main function of the somatic division

Motor neurons

Neurons that go into muscle

Sensory neurons

Neurons that connect with receptors

nope.

Can tissue regenerate in the CNS?

yes, but rate of regeneration is very slow (1.5mm/day)

Can tissue regenerate in the PNS?

1. Something causes the axon to break. The distal end fragments and degenerated and disappears.

2. Schwann cells work with macrophages to clear up fragments that are distal so it is a clean tube.

3. Axon filaments start to grow because Schwann cells release growth hormone to facilitate growth

4. Axon is regenerated, formation of new myelin sheath with Schwann cells.

4 Steps of nerve regeneration in PNS

31

How many pairs of spinal nerve roots are there?

12

How many pairs of cranial nerves are there?

Spinal nerve roots

Arise directly from the spinal cord. Motor and sensory to muscles of limbs and trunk

Cervical (8 pairs)

Spinal nerve roots for upper limb

Thoracic (12 pairs)

Spinal roots for thorax

Lumbar (5 pairs) and Saccral (5 pairs)

Spinal nerve roots for lower limb

Coccygeal (1 pair)

Spinal nerve roots for pelvic structures

Dorsal (posterior) horn

Horn that transmits sensory info

Ventral (anterior) horn

Horn that transmits motor info

Dorsal and ventral rami

A spinal nerve root is comprised of what?

Spinal nerve roots

Where is the start of the PNS?

Dorsal rami

What innervates the posterior trunk?

Ventral rami (because they are larger, more neurons)

What innervates upper and lower limbs, and anterior trunk?

Nerve plexus

Ventral rami from various levels crisscross and connect to for this complex nerve network

1. Each branch of the plexus has contribution from several spinal levels.

2. Fibers from each ventral rami travel to the periphery via several roots

3. Terminal nerves innervate all muscles of the limbs and anterior trunk
   SO that if there is damage to a single nerve root (ventral rami) then it will not paralyze the muscle

Functions of nerve plexuses [3]

Phrenic nerve (C3-C5) supplies the diaphragm

Nerve of cervical plexus

Axillary

Ulnar

Radial

Nerves of brachial plexus (upper limb) [3]

Ulnar nerve

Nerve that runs behind medial epicondyle. Provides sensory information to little finger and half of other finger(anterior)

Radial nerve

Posterior nerve that innervates all posterior arm muscle. Damage to the posterior nerve can mean losing the ability to extend wrist and elbow

1. Sciatic

2. femoral

3. Common fibular

Important nerves of lumbar plexus (lower limb) [3]

Sciatic nerve

Nerve in gluteal region. Largest nerve in the body. Reason that injections in this region are rarely done.

Femoral nerve

Anterior nerve that supplies muscles that enable knee extension. Ability to fight gravity.

Common fibular nerve.

Nerve that allows dorsiflexion of the ankle, and evertors. Subject to pressure.

Foot drop

inability to control dorsiflexion, feet slap when walking.

Dermatomes

Regions of the skin that are supplied by specific spinal nerves. Used clinically to determine area of nerve root injury. Tested by ability to detect touch.

Would contain motor and sensory fibers because nerve root has both

What type of fibers do dorsal rami contain?

Would contain motor and sensory fibers because nerve root has both.

What type of nerve fibers would ventral rami contain?

They arise from the underside of the brain, and get out through the many openings in the skull

Where to cranial nerves arise?

1. Sensory nerves that carry smell, vision, taste, and hearing

2. Sensory nerves that carry sensory info from inner ear (balance)

3. Sensory nerves for sensation of most of face

4. Motor neurons for eyes, facial expression, traps, tongue, swallowing, speech

5. Involved in parasympathetic system

What do cranial nerves do? [5]

Underside of the brain

where are cranial nerves located?

PNS

Are cranial nerves part of CNS or PNS?

Olfactory nerve

Cranial nerve that conveys sensory info for sense of smell

Optic nerve

Cranial nerve conveys sensory info for vision

Trigeminal nerve

Cranial nerve conveys sensory info to the whole face

Facial nerve

Cranial nerve for muscles of the face

Vestibulocochlear nerve

Cranial nerve carries hearing and balance info

1. Inborn

2. learned

Two types of refexes

Inborn reflexes

Rapid and predictable motor response to stimulus. Are unlearned, unpremeditated, involuntary

1. Tendon tap

2. Flexor withdrawal (something sharp, pull away)

Examples of inborn reflexes

Learned reflexes (sometimes called acquired reflexes)

Reflexes that result from practice or repetition, normally involve learning some complex motor skill

1. Driving a standard

2. Downhill skiing

3. Any complex skill you become very good at with practice

Examples of learned reflexes

1. Receptor

2. Sensory neuron: conveys sensory info to CNS

3. Integration center: can be spinal cord or multiple interneurons

4. Motor neurons: carries info out from integration center to the…

5. Effector: does the action

5 elements of a reflex arc

Stretch reflex

Stretches the muscle just a little bit. Receptors in the muscle sense the stretch (proprioceptors) and stimulate stretch receptors. When stimulated, generates action potential that causes muscle to contract. Thought to be a protective reflex

1. Sensory and motor connections between spinal cord and muscle are intact

2. Vigor of response tells you how excitable the motor neurons are.

What does normal stretch reflex indicate? [2]

1. Somatic ( body, affects skeletal muscle

2. Autonomic (innervate visceral effectors, glands, smooth muscle, cardiac muscle)

How can reflexes be classified? [2]

1. Patellar tendon (lower limb)

2. Biceps tendon (upper limb)

Two examples of stretch reflexes

Ventral horn or peripheral nerve damage

Clinical interpretation of hypoactive reflex

Lesions in CNS. These lesions can remove inhibitory input to motor neurons, causing them to be more excitable.

Clinical interpretation of hyperactive reflex

Flexor and cross extensor reflex

Stepping on something sharp, pull that leg away, use other leg to keep balance. (reflex that protects us from injury and falling. can be overridden).

Plantar reflexes

When a blunt object is run along the lateral, plantar surface of the foot from heal to toes. Non-patological response is flexion of the toes. Pathological response is extension of big toe and other toes fan (normal for infants under 1)

Tests integrity from L4 to S2

Where does plantar reflex test?

Umbilical reflex

Stoking the skin above, to the side, or below the umbilicus causes a contraction of abdominal muscles.

Tests integrity of spinal cord and ventral rami from T8-T12

Where does abdominal reflex test?