Peripheral

1 Sensory Receptors and Sensation

• Sensory Receptors – Respond to changes (stimuli) in the environment – Generate graded potentials that can trigger an that is carried to the CNS • Sensation – awareness of the stimulus • Perception – interpretation of the stimulus • Classification by Stimulus Type – Mechanoreceptors – Thermoreceptors – Photoreceptors – Chemoreceptors – nociceptors

2 Sensory Receptors and Sensation

• Classification by Location

– Exteroceptors – Interoceptors – Proprioceptors

• Classification by Structural Complexity

– Simple Receptors

• Modified dendritic endings • Found throughout the body • Monitor general sensation

– Complex Receptors

• organs (special )

3 Sensory Receptors and Sensation

• Simple Receptors of the General Senses

4 Sensory Receptors and Sensation

5 Sensory Receptors and Sensation

• Sensation to Perception – General Organization of the Somatosensory System – three major levels – Receptor Level Processing – sensory neurons • For a sensation to occur a stimulus must excite a receptor – Receptor specificity – Stimulus must be applied to the receptor’s receptive field (the smaller the field the better the brain can localize the stimulus) – Energy of the stimulus must be converted to a graded potential (receptor potential); called transduction – Generator potential of the first order neuron must reach threshold to be transmitted – Strength of stimulus is encoded in frequency (the faster the stronger) – Terminology

» Tonic receptors – usually firing at a particular rate constantly; stimulus changes the rate » Phasic receptors – usually off; stimulus turns them on » Adaptation – reduction in sensitivity to a stimulus

6 Sensory Receptors and Sensation

– Circuit Level Processing – ascending (sensory) pathways (tracts)

• Job is to deliver impulses the correct area of the cerebral cortex • Impulses first goes from the a nerve to the , ultimately to either the cerebellum or thalamus (second order neuron) • If the information is going to the cerebral cortex a third order neuron carries it from the thalamus to the appropriate area of the cerebral cortex

– Perceptual Level Processing – cerebral cortex, but also along the way – perception is defined by the region of the brain interpreting it not necessarily the stimulus – the brain interprets and projects where in the body the stimulus is coming from

7 Sensory Receptors and Sensation

– Main Aspects of Perception

• Perceptual Detection • Magnitude Estimation • Spatial Discrimination – two-point discrimination test • Feature Abstraction – interpreting several features of a perception to determine the actual “make-up” of the stimulus • Quality Discrimination – some modalities have different qualities, ex. taste; bitter, sour, sweet, salty • Pattern Recognition – misspelled sheet I handed out

8 Transmission Lines: Nerves and Their Structure and Repair

• Nerves and Associated Ganglia – Structure

9 Transmission Lines: Nerves and Their Structure and Repair

– Classification

• Sensory (afferent) nerves • Motor (efferent) nerves • Mixed nerves

– Ganglia

10 Transmission Lines: Nerves and Their Structure and Repair

– Regeneration of Nerve Fibers

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• Naming

– Use of Roman numerals I – XII

– Named according to structures served or function(s)

On occasion our trust truck acts funny – very good vehicle anyhow

Some say marry money but my brothers say bad business marry money

12 Spinal Nerves

• General Features

– 31 pairs – Naming

13 Spinal Nerves

– Anatomy

14 Spinal Nerves

15 Spinal Nerves

• Innervation of Specific Body Regions

– Dorsal Rami – supply skin and muscles of posterior trunk – Ventral Rami – anterior trunk and limbs

• All but T1 – T12 form plexuses

16 Cervical Plexus

17 Brachial Plexus

18 Skin of the inferior, lateral portion of the shoulder – m uscles of the lateral arm for rotation and abduction

19 Skin of posterior surface of the arm and forearm , lateral 2/3 of back of hand – m uscles for extension of elbow , extends w rist, fingers, thum b, supinates 20 forearm Skin of lateral surface of forearm – m uscles for elbow (flexion)

21 Skin of m edial 1/3 of hand, little finger, and m edial ½ of ring finger– m uscles for w rist (flexion), m ost intrinsic finger m uscles

22 Lateral 2/3 of palm of hand, thum b, index and m iddle finger, and the lateral ½ of ring finger, and dorsal tips of the sam e fingers – m uscles for forearm (pronation), w rist (flexion/abduction), finger (flexion)

23 24 Superior m edial side of thigh – m uscles for: thigh (lateral rotation/adduction), hip (flexion)

25 Anterior and lateral branches supply the anterior and lateral thigh; saphenous branch supplies the m edial leg and foot – m uscles for: thigh (flexion), leg (flexion, extension)

Carry inform ation concerning pain and tem perature 26 27 Branches from tibial nerve serve the sole of the foot and lateral and posterior 1/3 of leg and lateral side of foot – m uscles for: thigh (extension/adduction), leg (flexion), foot (plantar flexes), 28 (flexes) CaLrrayt etwraol- psouinrfta dcisec orifm kinnaeteio, ng, rperaotp raioncde psteiocno,n pdr etsoseu,r ed,o arnsda lv aibnrta.t itohni rd seonsf aletigon asnd top of foot – m uscles for: thigh (extension), leg 29 (flexion), foot (flexion/eversion), toes (extension) Dermatomes

30 Motor Endings and Motor Activity

• Peripheral Motor Endings – Innervation of - neuromuscular junctions

– Innvervation of Visceral (Smooth) Muscle and Glands

• Possess varicosities that typically contain either acetylcholine or norepinephrine

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• Arc

32 Spinal Reflexes

• Stretch and Golgi Tendon Reflexes – Functional anatomy

33 Spinal Reflexes

34 Spinal Reflexes

•

– Demonstrates reciprocal inhibition – Example is the knee-jerk or

• Monosynaptic • Ipsilateral • Gives us information concerning

– The status of both the sensory and motor pathway – The status of the spinal cord

35 Spinal Reflexes

36 Spinal Reflexes

• Golgi – Polysynaptic – Results in reciprocal activation

37 Spinal Reflexes

• Flexor (Withdrawl) Reflex/

38 Spinal Reflexes

• Superficial Reflexes – – blunt object stroked along lateral side of the plantar surface

• Test spinal cord segment (L4 – S2) • Integrity of corticospinal tracts • Normal response downward deflection of toes • Abnormal – Babinski’s sign – toes dorsiflex, smaller toes flare laterally – this is normal in children

– Abdominal Reflexes - stroke skin on lateral side of abdomen to the side, above or below the umbilicus • Normal – umbilicus should move towards stroked side

• Test cord segments (T8 – T12) • Integrity of corticospinal tracts

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