SENSATION

General

1. Sensation - awareness of changes in the internal or external environment

2. Perception - conscious interpretation of stimuli

Sensory modalities

1. Sensory modality – each unique type of sensation; touch, pain, vision, hearing

2. General senses – would include both

-a. Somatic senses – tactile, thermal, pain, and proprioception

-b. Visceral senses – information about internal organs

3. Special senses – smell, taste, vision, hearing, and balance

Process of Sensation

1. Receptor stimulation – specialized to respond to these different types of stimuli

2. Signal transduction – stimulus translated into a graded potential

-a. Generator potential – generates an action potential; usually nerve endings

-b. Receptor potential – graded potential releases neurotransmitters; usually separate cells

3. Impulse generation – graded potential reaches threshold

-a. Action potential – is generated

-b. First order neuron – conduct impulses from PNS to CNS

4. Sensory input integration – CNS receives and interprets

Sensory receptors

1. Location

-a. Exteroceptors - body surfaces: stimuli: touch, pressure, pain, temperature

-b. Interoceptors – viscera, blood vessels; chemical, tissue stretch, temperature

-c. Proprioceptors - musculoskeletal organs they monitor the degree of stretch

2. Stimulus detected

-a. Mechanoreceptors - nerve impulse when deformed by mechanical forces

-b. Thermoreceptors - sensitive to temperature changes

-c. Photoreceptors - respond to changes in light energy

-d. Chemoreceptors - chemicals in solution; smell and taste; blood chemistry

-e. Nociceptors - respond to damaging stimuli; most can be nociceptors

3. Structural complexity

-a. Separate cells – synapse with first order; inner ear, eye, taste bud

-b. Free nerve endings – pain, thermal, tickle, itch

-c. Encapsulated nerve endings – enhanced specificity

Free nerve endings

1. Free dendritic endings - most; nociceptors, thermoreceptors, mechanoreceptors

2. Merkel cells – modified free dendritic; associate epithelial cells; mechanoreceptor

3. Root hair plexus - basket of nerve; hair follicles; light touch from bending of hair

Encapsulated receptors

1. Meissner’s corpuscles - spiraling dendrites surrounded by Schwann cells

-a. Description - surrounded by a thin egg shaped connective tissue sheath

-b. Location - dermal papillae

-c. Function - they can discriminate light touch, particularly for hairless skin

2. Krause’s end bulbs - like Meissner’s corpuscles

-a. Location - connective tissue of mucosa, hairless skin near body openings

-b. Function - as Meissner’s corpuscles

3. Pacinian corpuscles - large; single dendrite; 60 layers of Schwann cells

-a. Location - lower dermis and subcutaneous tissue

-b. Function - deep pressure; stretch; vibration

4. Ruffini’s corpuscles - a spray of dendritic endings enclosed by a flattened capsule

-a. Location - deep in dermis, hypodermis, and joint capsules

-b. Function - exteroceptors and proprioceptors

5. Muscle spindles - fusiform; modified muscle fiber in a connective tissue capsule

-a. Function - detect when muscles are stretched; proprioceptors

6. Tendon organ - in tendons collagen fibers surrounded by dendrites

-a. Function -respond to tendon stretch; proprioceptors

7. Joint kinesthetic receptor - proprioceptors of joint cavity

-a. Description - Pacinian, Ruffini’s, naked nerve endings, Golgi tendon organ like

Adaptation

1. Adaptation – decrease in generator potential with constant stimulus

2. Rapid adapting receptors – monitor changes; pressure, touch, smell

3. Slowly adapting receptors – send impulse; pain, body position, blood chemicals

Pain

1. Fast pain – in skin; localized; pin prick

-a. Superficial somatic pain – also called this

2. Slow pain – skin and deeper; burning, aching, toothache pain

-b. Deep somatic pain – skeletal muscles, deep fascia, joints

3. Visceral pain – nociceptor in organs; very diffuse

-a. Referred pain – pain felt far from the target organ

CEREBRAL CORTEX

General

1. Primary soatosensory area – post central gyrus

2. Primary motor area – pre central gyrus

SOMATIC SENSORY PATHWAYS

General

1. First order neuron - cell body in dorsal root ganglion

2. Second order neuron - cell body in either the dorsal horn or the medulla

3. Third order neuron - cell body in thalamic nuclei; to cortex

Posterior column – medial lemniscus pathway

1. Posterior (dorsal) column – contain axons of the first order neuron; to medulla

2. Medullary nuclei – synapse with cell bodies of second order neurons in the medulla

-a. Gracile nucleus – synapses with 1^st order axons form lower body

-b. Cuneate nucleus – synapses with 1^st order axons form upper body

3. Medial lemiscus – contains axons of 2^nd order neurons; to thalamus

4. Thalamus – nuclei contain cell bodies of third order neurons; axons to cortex

5. Sensations – highly refined and evolved

-a. Fine touch – very specific information

-b. Stereognosis – size, shape, texture

-c. Propriocepion – location of body part

-d. Vibration – rapidly fluctuating touch stimuli

Anteriolateral (spinothalmic) pathway

1. First order neuron – synapses with second order neuron

2. Second order neuron – cell body found in posterior horn; axons to thalamus

3. Third order neurons – cell body in thalamic nucleus; to cortex

4. Sensations – nonspecific pain, thermal, tickle, and itch

Spinocerebellar pathways

1. First order sensory – proprioceptors in muscle

2. Second order sensory – in spinal cord dorsal horn; to cerebellum

3. Cerebellum - coordinate skeletal muscle; no somatosensory; unconscious

SOMATIC MOTOR PATHWAYS

General

1. Lower motor neurons – axons leave CNS to skeletal muscles

2. Somatic motor pathways – four circuits; input to lower motor neuons

-a. Local circuit neurons – nearby interneurons

-b. Upper motor neurons – from cortex and brain stem

-c. Basal ganglia neurons – control upper motor neurons

-d. Cerebellar neurons – also control upper motor neurons

Direct motor pathways

1. Voluntary movement – control these

2. Pyrimadal pathway – also known as this

3. Upper motor neurons – primary motor area; premotor; and primary somatosensory

4. Tracts – include

-a. Lateral coricospinal tracts – highly skilled movements of limbs, hands, and feet

-b. Anterior corticospinal tracts – neck and trunk movement

-c. Corticobulbar tract – precise head, neck, face, eye, and tongue movement

Indirect motor pathways

1. Extrapyramidal pathways – other name

2. Complexity – synapse with neurons from cortex, cerebellum, basal ganglia, brain stem

Basal ganglia

1. Feedback circuit – cortex, to basal ganglia to thalamus to cortex

2. Movement – initiation and termination

3. Unwanted movements – are suppressed

4. Other functions – sensory, cognitive, limbic, and linguistic

5. Parkinson disease – increased muscle tone in head, face, and legs

6. Huntington disease – rapid jerky movements

Cerebellum

1. Skilled movements – both learning and performing

2. Posture – is maintained

3. Equilibrium – also involved in this

4. Ataxia – movement is jerky and uncoordinated; speech is slurred

5. Intention tremor – shaking during voluntary movement

INTEGRATIVE FUNCTION OF THE CEREBRUM

Sleep: patterns

1. Circadian rhythm – alternating cycle of sleep and wakefulness during a 24 hour period

2. Hypothalamus – contains the biological clock which sets the timing of the sleep pattern

3. Reticular activating system – part of the reticular formation

-a. Sleep – activity declines, sleep begins; cortex less stimulated

-b. REM – mediated by reticular activating system

-c. Arousal – reticular activating system stimulated by sensory input, like alarm clock

Sleep: stages

1. Sleep - stage of changed consciousness, partial unconsciousness: can be aroused from

2. NREM Stages – non rapid eye movement sleep

-a. Stage 1 - mostly alpha waves; easy to arouse

-b. Stage 2 - EEG more irregular; arousal more difficult

-c. Stage 3 - theta and delta waves appear; 20 min after stage 1 sleep; dreaming common

-d. Stage 4 - theta waves; vital signs; sleep walking, bedwetting occur; arousal difficult

3. REM - paralysis; most dreaming, Alpha waves;↑ HR, brain O₂ use; like awake

Sleep: patterns

1. Sleep pattern - in young and middle aged adults

-a. NREM- stage 1 to stage 4 of sleep

-b. REM - each cycle takes about 90 minutes; REM becomes longer with each cycle

2. Importance – different types may have benefits

-a. Slow wave sleep - may have restorative effect as most neural mechanisms slow down -b. REM sleep - work through emotional patterns; get rid meaningless communications

Learning and Memory

1. Learning – ability to acquire new information

2. Memory – learned information is stored and retrieved

3. Immediate memory – ability to recall information about an ongoing experience

4. Short term memory – fleeting; telephone number; particular student, limited capacity

5. Long term memory – fairly unlimited; can last for years

6. Memory consolidation – reinforcement from retrieval; short to long term memory

5. Mechanisms - involve

-a. Long-term potentiation – enhanced transmission between neurons

-b. NMDA receptors – glutamate binds; postsynaptic releases NO; to presynaptic