Neuro Week 5

autonomic nervous system and somatosensory systems

The autonomic nervous system (ANS) is critical for survival because it regulates ______ and ______

Homeostasis, reproduction

Homeostasis

maintenance of an optimal internal environment

The ANS regulates the ______, ______, and _____

viscera (internal organs), vasculature (smooth muscle), and glands

The ANS supports (5)

1. circulation and respiration

2. digestion and metabolism

3. secretions

4. body temperature

5. reproduction

4 aspects of autonomic function

1. receptors detect changes inside and outside the body

2. afferent pathways carry information toward the central nervous system

3. central regulation integrates the information and selects a response

4. efferent pathways carry sympathetic, parasympathetic, or hormonal output to effectors

Afferent pathways

• Arriving at the CNS

• Sensory information

Efferent pathway

• Exits the CNS

• Motor information

Autonomic receptors (4)

1. Mechanoreceptors

2. Chemoreceptors

3. Nociceptors

4. Thermoreceptors

Mechanoreceptors

Respond to pressure and stretch

• baroreceptors monitor blood pressure

• visceral stretch receptors monitor distention of organs such as the bladder and intestines

Chemoreceptors

Respond to chemical concentrations

• monitor oxygen, carbon dioxide, pH, blood glucose, and electrolytes

Nociceptors

Respond to stimuli that threaten or damage tissue

• visceral nociceptors may respond to stretch, ischemia, or irritating chemicals

Thermoreceptors

Respond to heating or cooling

• hypothalamus monitors blood temperatures

• cutaneous receptors detect external temperature changes

From receptor to response (4)

1. autonomic receptors detect a change in the internal or external environment

2. afferent information enters the CNS through spinal nerves or cranial nerves IX (9) and X (10)

3. information carried by cranial nerves IX and X converges in the solitary nucleus of the medulla. Other autonomic information is processed in the spinal cord and additional brain regions

4. sympathetic, parasympathetic, and hormonal outputs adjust organ function

Receptor to response step 1

autonomic receptors detect a change in the internal or external environment

Receptor to response step 2

afferent information enters the CNS through spinal nerves or cranial nerves IX (9) and X (10)

Receptor to response step 3

information carried by cranial nerves IX and X converges in the solitary nucleus of the medulla. Other autonomic information is processed in the spinal cord and additional brain regions

Receptor to response step 4

sympathetic, parasympathetic, and hormonal outputs adjust organ function

Key idea regarding autonomic control

autonomic control is distributed across multiple levels of the nervous system

Central regulation of autonomic function- MEDULLA

contains autonomic control areas that regulate heart rate, blood pressure, respiration, vasoconstriction, and vasodilation. It sends output through the spinal cord and vagus nerve

Central regulation of autonomic function- PONS

contains areas involved in regulating respiration and works with the medulla to control breathing

Central regulation of autonomic function- HYPOTHALAMUS

serves as the master controller of homeostasis. It influences cardiorespiratory function, metabolism, body temperature, water balance, digestion, endocrine activity, and reproductive behavior

Central regulation of autonomic function- EMOTION AND MOTIVIATION SYSTEM

influences autonomic responses associated with emotion, mood, and motivation. It modifies activity in autonomic control areas rather than directly controlling individual organs

Somatic motor system (3)

1. activation is usually voluntary

2. skeletal muscle requires somatic motor input to contract normally

3. one neuron travels from the CNS directly to skeletal muscle

Autonomic efferent systems (3)

1. regulation is usually nonconscious and can also be influenced by hormones

2. many internal organs can continue functioning independently of direct CNS input

3. usually a two-neuron pathway (preganglionic neuron → autonomic ganglion, postganglionic neuron → effector

Two autonomic divisions

1. sympathetic nervous system

2. parasympathetic nervous system

Sympathetic nervous system (5)

1. mobilize resources

2. thoracolumbar outflow: T1-L2

3. maintain optimal blood supply and prepare the body to meet changing demands (primary role)

4. often activated broadly as a system

5. fight, flight, or freeze

Parasympathetic nervous system (5)

1. conserve resources

2. craniosacral outflow: brainstem and S2-S4

3. energy conservation, storage, digestion, and routine maintenance (primary role)

4. produces more discrete effects on individual organs

5. rest and digest

Sympathetic functions (6)

continuously helps maintain blood pressure, blood flow, and body temperature

1. increases heart rate and force of contraction

2. redistributes blood flow to support active organs and skeletal muscle

3. dilates the pupils and airways

4. increases sweating

5. increases glucose availability and metabolic activity

6. decreases gastrointestinal motility and secretions

Parasympathetic functions (6)

slow, controlled breathing can increase parasympathetic influence and support calming

1. the Vagus nerve carries most parasympathetic output to the thoracic and abdominal organs

2. decreases cardiac activity

3. facilitates digestion and glandular secretions

4. constricts the pupil and supports near vision

5. promotes emptying of the bowel and bladder

6. supports erection and lubrication

Sweat glands and most blood vessels are regulated primarily by the

Sympathetic system

Sympathetic effect of the

• eyes

• heart

• lungs

• gastrointestinal tract

• bowel and bladder

• dilates the pupil

• increases rate and force

• dilates bronchi

• decreases peristalsis and secretions

• inhibits emptying

Parasympathetic effect of the

• eyes

• heart

• lungs

• gastrointestinal tract

• bowel and bladder

• constricts the pupil and increases lens curvature

• decreases rate

• constricts bronchi and increases secretions

• increases peristalsis and secretions

• promotes emptying

Tropic skin changes + clinical relevance

• occur when loss of autonomic innervation alters vascular control, temperature regulation, and sweating in the affected region

• Inspect skin carefully, protect areas with altered sensation, and monitor healing and tissue integrity

Tropic skin changes; possible findings

• skin

  • altered elasticity or thickness

  • color changes

• temperature & sweating

  • abnormal skin temp

  • increased, decreases, or absent sweating

• hair and nails

  • changes in hair growth

  • changes in nail formation

Orthostatic hypotension

a decrease of at least 20 mm Hg systolic blood pressure or 10 mm Hg diastolic blood pressure within the first 3 minutes after moving from supine to standing

Orthostatic hypotension mechanism

gravity causes blood to pool in the lower limbs, reducing venous return, cardiac output, and arterial pressure

Orthostatic hypotension common symptoms

• dizziness

• light-headedness

• fainting

• fatigue

• feeling “about to faint”

Neurogenic orthostatic hypotension

• occurs when autonomic pathways cannot produce an adequate vasoconstrictor response

• causes may include spinal cord disorders, autonomic degenerative disorders, and peripheral neuropathies

Postural orthostatic tachycardia syndrome (POTS)

common type of autonomic dysfunction marked by intolerance to standing

POTS ages and heart rate

• heart-rate changes within 10 minutes after moving from supine to standing

• adults

  • heart rate increases by 30 beats/min or more

• ages 12-19

  • heart rate increases by 40 beats/min or more

Typical criteria for POTS (3)

1. symptoms occur with standing

2. orthostatic hypotension is absent

3. no other explanation accounts for the tachycardia

Symptoms of POTS

• light-headedness

• fatigue

• headache

• palpations

• nausea

• irritability

• cognitive difficulty

Therapeutic exercise for POTS

• reclined/recumbent exercise

  • exercise may begin in a reclined or horizontal positions (Ex: rowing, swimming, & recumbent bicycling)

• sitting

  • progress gradually to sitting exercise

• standing

  • progress to standing exercise according to the persons tolerance

POTS clinical principal

use a graded progression toward upright activity rather than beginning with prolonged standing exercise

• monitor symptoms, heart rate, blood pressure, hydration, and recovery

Is a medical emergency requiring immediate intervention

Autonomic dysreflexia

who is at risk for autonomic dysreflexia

people with spinal cord injury at or above T6, particularly those with cervical injuries

Autonomic dysreflexia happens when

a noxious stimulus below the level of injury triggers an excessive sympathetic response. because descending inhibitory signals cannot pass the spinal cord lesion, severe vasoconstriction and hypertension develop below the injury

Signs and symptoms of autonomic dysreflexia

• sudden, sever hypertension

• pounding headache

• bradycardia (slowed heart rate)

• flushing & sweating above the injury

• pale, cool skin below the injury

• nasal congestion, anxiety, or blurred vision

5 step explanation of what is happening during autonomic dysreflexia

1. a noxious stimulus below the injury triggers a massive sympathetic response

2. vasoconstriction below the injury causes systemic hypertension

3. baroreceptors detect the hypertension

4. the brain increases vagal activity, often slowing the hypertension

5. descending corrective signals are blocked at the SCI

autonomic dysreflexia

what is happening…

• below the injury

• above the injury

• systemic effect

• unopposed sympathetic vasoconstriction

• compensatory vasodilation, flushing, and sweating

• sever hypertension, often with reflex bradycardia

Immediate response to autonomic dysreflexia (5)

1. stop the activity and sit the person upright, with the legs lowered if possible

2. loosen restrictive clothing and equipment

3. monitor blood pressure and heart rate frequently

4. identify and remove the trigger, checking the bladder first, followed by the bowel and skin

5. follow the person’s emergency plan and obtain urgent medical assistance if blood pressure remains elevated or the trigger cannot be removed

For autonomic dysreflexia, do not place the person _____, this may further _____ blood pressure. Do not leave the person unattended

supine, increase

Somatosensation allows us to (3)

1. explore and understand the external world

2. control movement accurately

3. protect the body from injury

somatosensory information begins at receptors in the _____, ______, ______, _____, and other tissues

skin, muscles, tendons, joints

Sensation

awareness of stimulus detected by sensory receptors

Perception

the brains interpretation of sensory information, allowing the stimulus to become meaningful

Sensation provides the ____; perception gives the input _____

input, meaning

Perception is an active interaction between the _____, ____, and the____

brain, body, environment

3 neuron relay

peripheral receptor -1st order→ spinal cord or brainstem -2nd order→ thalamus -3rd order→ cerebral cortex

first order neuron

carries sensory information from a peripheral receptor into the spinal cord or brainstem

second order neuron

carries information from the spinal cord or brainstem to the thalamus

third order neuron

carries information from the thalamus to the cerebral cortex

the cell bodies of first-order somatosensory neurons from the body are located in the _____ _____ ____

dorsal root ganglia

Dorsal root

sensory information enters the spinal cord

dorsal root ganglion

contains the cell bodies of first order sensory neurons

dorsal horn

receives and begins processing sensory information

ventral root

motor information leaves the spinal cord

spinal nerve

contains both sensory and motor fibers

sensory comes in the back (_____), motor comes out the front (____)

dorsal, ventral

3 types of cutaneous information

1. touch and pressure

2. nociception

3. temperature

touch and pressure (2)

mechanoreceptors

1. includes light touch, vibration, skin stretch, and superficial pressure

2. supports discriminative touch and stimulus localization

nociception (2)

nociceptors

1. detects stimuli that threaten or damage tissue

2. contributes to protective responses and the experience of pain

temperature (2)

Thermoreceptors

1. detects warming and cooling of the skin

2. supports protection and temperature regulation

Tonic receptors (3)

1. slowly adapting

2. continue responding while a stimulus remains present

3. provide information about the duration and ongoing intensity of a stimulus

Ex; merkel cells, ruffini endings, & many nociceptors

Phasic receptors

1. rapidly adapting

2. respond most strongly when a stimulus begins, ends, or changes

3. becomes less responsive when a constant stimulus remains present

Ex; Meissner corpuscles, Pacinian corpuscles, and hair-follicle endings

the area of skin in which stimulation activates a particular sensory neuron

receptive fields

Fingertips (4)

1. many sensory receptors

2. small receptive fields

3. two closely spaced points are more likely to activate separate neurons

4. the person is more likely to perceive two distinct points

Shoulder or back (4)

1. fewer sensory receptors

2. larger receptive fields

3. the same two points may fall within on receptive field

4. the person may perceive one point

provide more precise sensory localization and better two point discrimination

smaller receptive fields

Dermatome (3)

1. an area of skin supplied primarily by one spinal nerve root

2. a dermatomal sensory loss patterns suggests spinal nerve root involvement

3. adjacent dermatomes overlap, so injury to one root may reduce sensation without causing complete anesthesia

Peripheral nerve distribution (3)

1. an area of skin supplied by a named peripheral nerve (like radial or ulnar nerve)

2. each peripheral nerve contains fibers from multiple spinal nerve roots

3. sensory loss matching a named nerve suggests a peripheral nerve lesion

A peripheral nerve contains fibers from ____ spinal nerves, so its _____ distribution does ____ match a single dermatome

multiple, sensory, not

Proprioception

provides information about body position and movement

proprioceptive receptors

1. muscle spindles

2. Golgi tendon organs

3. joint receptors

muscle spindles

• located within skeletal muscle

• detect

  • muscle length

  • changes in muscle length

  • velocity of stretch (how quickly the muscle length changes)

• role

  • provides information for proprioception

  • contribute to the stretch reflex

  • help regulate muscle tone and postural control

stretch reflex

stretching a muscle activates its muscle spindles, producing sensory input to the spinal cord and reflex contraction of the stretched muscle

Golgi tendon organs

• are sensory receptors located within collagen fibers near the musculotendinous junction

• detect

  • tension or force within the tendon

  • tension produced by active muscle contraction

  • tension produced by passive stretch of the musculotendinous unit

• provide the CNS with feedback about how much force a muscle is producing

Clinical takeaway for herpes zoster

a unilateral dermatomal pattern of pain and rash suggest involvement of a sensory ganglion and spinal nerve distribution

postherpetic neuralgia

is pain that continues after the shingles rash has resolved

Herpes zoster and postherpetic neuralgia

• after chickenpox, the varicella-zoster virus remains latent in a dorsal root ganglion or cranial nerve sensory ganglion

• reactivation produces herpes zoster, or shingles

• the painful rash is usually unilateral and follows one or two adjacent dermatomes

• because sensory ganglia are primarily affected, the predominant symptoms are usually sensory, including pain, burning, tingling, or hypersensitivity

• postherpetic neuralgia

coordinated movement requires both accurate _______ _____ and effective ____ _____. A problem with either can produce _____

proprioceptive input, cerebellar processing, ataxia

Sensory ataxia: input problem (5)

1. proprioceptive information does not reach the CNS accurately

2. the cerebellum receives insufficient information about body position and movement

3. vision can partially compensate

4. balance becomes substantially worse when the eyes are closed

5. may produce a positive Romberg sign

   1. open → closed: sway increases

Cerebellar ataxia: processing problem (4)

1. proprioceptive input may remain intact

2. the cerebellum cannot effectively coordinate and correct movement

3. vision cannot fully compensate

4. balance is impaired with eyes open and remains impaired with eyes closed

   1. open → closed: no change

3 types of somatosensory pathways

1. conscious relay pathways

2. divergent pathways

3. nonconscious relay pathways

conscious relay pathways (3)

1. destination: cerebral cortex

2. carry high-accuracy, somatotopically organized information

3. support conscious perception & accurate localization of sensation

Divergent pathways (3)

1. destinations: multiple brain regions

2. carry less precisely localized information at conscious and nonconscious levels

3. influence arousal, emotion, autonomic response, and the broader experience of paint

nonconscious relay pathway (3)

1. destination: cerebellum

2. carry movement-related proprioceptive information that does not reach conscious awareness

3. support nonconscious regulation of posture, coordination, and ongoing movement correction

What dorsal column medial lemniscus pathway carries (2)

1. light touch, including localization, vibration, and two-point discrimination

2. conscious proprioception

Pathway of the DCML (4)

1. peripheral receptors activate first order neurons

2. first order neurons enter the spinal cord and ascend on the same side in the dorsal columns

3. in the medulla, they synapse with second order neurons. the second order neurons cross to the opposite side (decussate) and ascend through the medial lemniscus to the thalamus

4. third order neurons carry the information from the thalamus to the primary somatosensory cortex

The DCML pathway crosses in the

Medulla