Spinal cord and sensory part of nervous system

Monitor the internal and external environment

Transmits signals from CNS to periphery

Control of movement

Transmits peripheral signal to CNS for processing

Regulation of internal organs

Touch

Pain

Vision

Hearing

Smell

Thermal sensation

Proprioception

Taste

Vision

Hearing

Taste

Pain

Smell

General senses have receptors distributed over a large part of the body

General senses have receptors within specific organs

General senses located in skin, muscle and joints are somatic (touch, pain, temp, etc..)

General senses located in internal organs are visceral (pain and pressure)

Balance is not a special sense

Stimulation, Perception, Transduction, Transmission

Stimulation, Transmission, Perception, Transduction

Stimulation, Transduction, Transmission, Perception

Stimulation, Transmission, Transduction, Perception

Somatic and olfactory senses reception is through secondary sensory neurons

General secondary receptors release neurotransmitter that bind to a neuron that transmits info to brain

Special secondary receptors release neurotransmitter that bind to a neuron that transmits info to brain

In taste, hearing, sight and balance it is through specialized epithelial receptor cells - secondary receptor.

Exteroreceptors - associated with skin

Proprioceptors - associated with joints, tendons, muscle, vestibular system

Visceroreceptors - associated with organs

Exteroreceptors - associated with organs

Nociceptors - respond to changes in temperature

Thermoreceptors - extreme mechanical, chemical, or thermal stimuli. Pain sensation

Mechanoreceptors: compression, bending, stretching of cells. Touch, pressure, proprioception, hearing, and balance sensation

Chemoreceptors - chemicals become attached to receptors on their membranes. Smell and taste sensation

Photoreceptors - respond to light. Vision

PROPRIOCEPTION – profound

EKSTEROCEPTION – superficial

INTEROCEPTION – special

TELECEPTION – visceral

Modality (type of sensation; touch, pain)

Location

Intensity

Timing - When stimuli starts

Reflex

EPICRITIC SENSATION – identification, localisation, characteristic, strength of stimulus possible

PROTOPATHIC SENSATION – identification, localisation, characteristic, strength of stimulus possible

PROTOPATHIC SENSATION – impossible precise identification of stimulus; often connected with impairing factors - crude touch, pain, extreme temperature

EPICRITIC SENSATION – impossible precise identification of stimulus; often connected with impairing factors - crude touch, pain, extreme temperature

Modality is encoded by a single pathway.

Each pathway encodes one specific sense

Each type of sensation (touch, sound, light, etc.) is called modality of sensation

Different modality of sensation is transmitted by a specific nerve fiber and determined by where the nerve fiber terminates in the brain

Receptors fires action potential only when stimulus impinges on the receptive field.

Fine resolution requires large receptive fields

Coarse resolution requires fewer receptive fields to cover the same body surface area

Receptive field in skin differ in size and response to touch

Coarse resolution; Certain regions of the body, such as arms & legs, have such very large receptive fields.

Coarse resolution; Two stimuli separated by as much as 40 mm will be perceived as a single point

Coarse resolution; Sensitive regions of the body with small secondary receptive fields include the fingertips.

Coarse resolution; Two stimuli separated by as little as 2 mm will activate separate pathways and will be perceived as distinct stimuli

Meissner occupy small receptive fields

Paccini occupy large receptive fields

Primary neuron response is improper to stimulus strength

lateral inhibition - adjacent relay cells are inhibited from firing by the excited relay cell

feed forward inhibition - primary sensory cell inhibits directly adjacent relay cells.

Lateral inhibition increases stimulus contrast

Population code - more sensory receptors are activated as stimulus gets greater

Intensity is encoded through the firing rate of receptors

Duration of action potential code for underlie perception of stimulus strength

Frequency of the stimulus is encoded by the time course of firing

Duration of the stimulus is encoded by the time course of firing

Phasic receptors - long-lasting stimulus will produce a prolonged repetitive discharge in the primary afferent neurons. (pain)

Phasic reseptors - long-lasting stimulus will produce a short-lived response in the primary afferent neurons.

Tonic receptors are fast-adapting

Baroreceptors

Paccinian corpuscles

Nociceptors

Poprioceptors

Tactile receptors (mechanoreceptors) - receptors detect position and movement

Thermal receptors - stimuli: heat and cold

Nociceptors - stimuli: painful touch, cut, extreme temperatures

Proprioceptive - stimuli: touch, pressure, vibration

Static proprioceptors - tonic discharge

Static proprioceptors - phasic discharge

Stimulus: deep cutaneous pressure; vibration

Located in epidermis

Lamellated corpuscles, single dendrite to layers of corpuscles arranged like

Pacini's corpuscle is a skin, sensory nerve ending

Slow adapting

Has a two-point discrimination. Ability to detect simultaneous stimulations at two points on the skin.

Rapidly adapting

Numerous and close together on thigh and chest

Used to determined temp of objects.

Axonal branches end as flattened expansions associated with epithelial cells

Responsible for steady-state signals (continuous touch)

Slowly adapting

Basal layers of hypodermis

Light touch and superficial
pressure

Primarily in dermis of fingers

Rapidly adapting

Respond to continuous touch or pressure

Slowly adapting

Does not respond to bending of hair as occurs in light touch

Hair end organs

End organ receptor fields overlap; sensation not very localized, yet very sensitive

Respond to bending of hair as occurs in light touch

Simplest, most common sensory receptor

Scattered through most of body; visceroceptors are of this type.

Picks up warm 10-15 times more numerous than cold

Pain: respons to freezing cold and burning hot, cut of skin, painful touch

Rapidly adapting

Large receptive area

Warm receptors: up to 30C, max excitability at 44-46C;

Thermal signals are transmitted in pathways same to those for pain signals

Cold receptors: max excitability at 24-28oC;

Warm sensation - Transmission by C fibers

For each 10C change metabolic rates (temp) alters intracellular chemical reactions more than 2-fold.

Cold sensation - Transmission by C fibers

Cold sensation - Transmission by Aδ

Provide information about tension of muscles

3-10 specialized intrafusal skeletal muscle cells

Provide information about length of muscles

Involved in stretch reflex

Proprioceptors associated with tendons

Respond to increased tension on tendon

Involved in invers stretch reflex

Provide information about length of muscles

Lateral inhibition - Key attributes of the stimulus must be represented in the signals of the primary SN

Stimulus transduction - Stimulus energy is converted into electrochemical energy

The stimulus information must be encoded into an electrical signal of some sort. These will result in information about intensity, duration, and location.

Neural encoding - sensory information must be fine tuned to achieve maximal discriminative capacity

Parallel pathways

Relay nuclei and Interneurons

Hierarchical organisation - different levels (highest at the head)

Spinal cord and fiber types

Neural maps - Parts of brain for different sensations

Transmission has specificity and follows topographical organisation

Cross-over to decussate through 2 major pathways; Dorsal column and anterolateral pathway.

Starts in the neurons of dorsal root ganglia

Ends in thalamus nuclei

Ia = Annulo-spiral ending of muscle spindle - A-alpha Fiber

Ia = Golgi tendon organ - A-alpha Fiber

II = Flower-spray ending of muscle spindle - A-beta Fiber

III = Pain, temp and other receptors - Cdr Fiber

Sensory supply to skin

All impulses from the receptors first enter the peripheral afferent nerve fiber.

After entering the Dorsal Roots it enters spinal ganglion

Terminates in spinal cord

Each dermatome is innervated by 2 segments of the spinal cord.

Ventral columns

Dorsal columns

Lateral and Anterior spinothalamic tract

Anterior and posterior spinocerebellar tracts

Spino-olivary cerebellar tract and Trigeminothalamic tract

Primary neurons have cell bodies in dorsal root ganglion.

Fasciculus gracilis: sensations from inferior to midthoracic level.

Fasciculus gracilis : impulses from above midthorax.

Carries sensations of two-point discrimination, proprioception, pressure, vibration to cerebrum, and cerebellum

Axons enter spinal cord and ascend to the medulla oblongata by decussating where they synapse with secondary neurons.

Picks up pain and temperature

Follows a 3 neuron system, where the primary neuron starts in dorsal root ganglia

Secondary neuron - thalamus VPL nucleus

Tertiary neuron - posterior horn neuron

Heat

Tickle

Itch

Crude touch

Pressure

Fibers join the spinothalamic tract in the brainstem

Involves Cranial nerve VI

In thalamus synapses on VPL nucleus

Carries similar information to that of the spinothalamic and dorsal-column/medial- lemniscal system

Carries info from face, Nasal cavity and Oral cavity

Spino-reticular tract to superior olivary nuclei

Spinal dorsal columns to nuclei of the medulla

Starts as climbing fibers on Purkinje cells

Spino-olivary - contribute to coordination of movement associated with balance

Both impulses from Spino-reticular tract and Spinal dorsal columns go to cerebellum

Anterior - sensation = Proprioception of muscle,
tendon, Joints receptors . Large tactile skin sensation

Anterior - sensation = Efferent copy of the anterior
horn motor drive

Posterior - termination = The same side as its origin. Mossy fibers on cerebellar cortex granular cells

Posterior - termination = Both side of cerebellum. Mossy fibers on cerebellar cortex granular cells

Cerebellum may reduce the conscious perception of sensations

Cortex may reduce the conscious perception of sensations

Spinotectal - involved in reflexes that turn the eyes and the head toward point of cutaneous stimulation

Corticospinal tracts send branches to ascending tracts and release neuromodulators such as endorphins

Corticospinal tracts send branches to descending tracts and release neuromodulators such as endorphins

Includes areas 3a, 3b, 1, and 2 in postcentral gyrus of the cortex

Topographic (somatotopic) projection = the feet - near the midline of the brain,

Topographic (somatotopic) projection = the feet - laterally, near the lateral fissure.

The cells of the S1 cortex are organized in columns specific to a particular modality.

The receptive fields of neurons contain only excitatory zones.

Regions needing low resolution are represented in the brain in fine detail

Regions of the body most richly supplied with sensory receptors have the largest number of neurons in the related areas of the neocortex.

High resolution is achieved by having many small receptive fields on the body surface

A larger representation in the cortex occurs when less neurons are dedicated to a region of the body.

Areas 3b, 1- respond to slowly adapting cutaneous receptors

Area 1- Deep skin receptors

Area 2 - deep skin receptors

Area 3a - muscle spindle, tendon and joint receptors

...to localize sensations discretely and judge pressure and weight

...to judge shapes and forms and to recognize the position of parts of the body.

...to judge taste and smell

...to judge texture of material and fine gradations in temperature

Impulses come from the ventral column system

Impulses come from the spinothalamic system and S1 area

Located in postcentral gyrus - posterior and inferior part (area 40 of the cerebral cortex).

Localization in this area is good.

Lesion to this area cause inability to recognize own body on same side as the lesion

Located behind the S1 area - areas 5 and 7

Lesion to this area cause inability to recognize own body opposite to the lesion

Lesion of this area lead to inability to recognize the complex forms (feeling for the shape of one's own body is lost).

Visual cortex: occipital lobe

Olfactory cortex: superior surface of prefrontal lobe

Primary auditory cortex: inferior part of temporal lobe

Taste area: lower tip of postcentral gyrus

Sensory neuron

Dorsal root ganglion

Efferent neuron

Interneurons of CNS - most reflexes go through these

Have both inhibitory and excitatory function

Slow neuron

Produce action potential

Hard neuron to excite

Fast conduction (120m/s)

From one node of ranvier to another

Slow conduction (3m/s)

Unmyelinated conduction

In spinal cord conduction goes uni-aterally between anterior and porsterior root, in one direction only.

Anterior spinal nerve roots contain only motor fibers

Posterior spinal nerve roots contain only sensory fibers

In spinal cord conduction goes bi-laterally between anterior and porsterior root

Somatic motor reflex - goes to viscera

Somatic motor reflex - goes to muscle and skin

Autonomic motor reflex - goes to viscera

Autonomic motor reflex - goes to muscle and skin

Large reflex arc

One synaps between sensory and motor neuron

Starts in Ia afferent fibers from muscle spindle

Complicated reflex

Duration of the knee jerk 19-24 ms.

Each muscle spindle consists of 10 muscle fibers enclosed in a connective tissue capsule

Nuclear bag fibers - thicker, 2 per spindle

Nuclear chain fibers - thicker, 2 per spindle

Primary - annulospiral endings – rapidly conducting Ia (A-alpha) afferents

Secondary - annulospiral endings – rapidly conducting Ia (A-alpha) afferents

Static (tonic) response of the nuclear bag region (rapid discharge after fast stretch, less rapid during sustained stretch)

Dynamic (phasic) response of the nuclear chain region (discharge at an increased rate throughout the period when the muscle is stretched).

Intrafusal muscle fibers - have gamma-motor neurons (S, D)

Extrafusal muscle fibers - have alpha-motor neurons

Only the ends of the muscle spindle contract, due to lack of actin and myosin in the centre

The mid-portion of the muscle spindle can stretch

Gamma motor neurons contract extrafusal muscle fibers and plates, contracting outer part of muscle spindle

Ia fibers only gives nuclear chain fiber

Dynamic response –increase spindle sensitivity to steady stretch

Gamma motoneurons cause contraction of spindle- stretch of nuclear bag portion – activation of Ia – reflex

Gamma discharge increases with alpha discharge

Static response - increase spindle sensitivity to rate of stretch

Gamma discharge with muscle stretch – increase of discharge in Ia

Dynamic response – decrease spindle sensitivity to
rate of stretch

Control – descending tracts from CNS – postural control

Gamma discharge decreases with alpha discharge

Sensory innervation: Ib - EPSP on motor neurons via interneurons

Activation: passive stretch, active contraction of
muscle

Receptors: in muscle spindle (nerve endings among fascicles of tendon)

Very high muscle tension produces – cessation of contraction (autogenic inhibition)

Regulate muscle force

Receptor: in muscle

Stimuli - nociceptive, noxious, painful

Response - flexor muscle- contraction (limb is moved away from the range of the irritating stimulus), extensor – inhibition

Effectors - recruitment of motor units – after discharge

Center - inhibition of stimulus in spinal cord

Regulation of the sensory function, contains motor centers and efferent pathways.

Regulation of the motor function, contains sensory centers and efferent pathways

Spinal modulation of impulses performed by sensory, motor, and interneurons in particular spinal segment

Spinal modulation of impulses performed by sensory, motor, and interneurons among various spinal segments

Grey matter – neural centers for somatic-motor & sensory, and autonomic-motor & sensory

White matter – neural centers for somatic-motor & sensory, and autonomic-motor & sensory

Grey matter – neural pathways afferent and efferent

White matter – neural pathways afferent and efferent

Convergence and divergence

After-effect

Contraction and relaxation

Summation and facilitation

Inhibition

alpha-motor neuron is a final common pathway, it connects impulses

Central inhibition - presynaptic is only EPSP

Central inhibition - Postsynaptic and autoinhibition are EPSP

Central inhibition - Autoinhibition is IPSP and mediated by renshaw cells

Inhibitory interneurons modulating alpha-motoneurons through (IPSP) renshaw cells

Inhibitory interneurons in stretch reflex.

Inhibitory interneurons in inverse-stretch reflex.

Inhibitory interneurons in withdrawal reflex.

Use glycine in its synapses

Crosses midline and ascends to brain stem reticular formation

Projects bi-laterally through intralaminar nuclei of the thalamus to regions of the cerebral cortex

Plays major role in general alertness and arousal in response to tactile (painful) stimuli

Does not cross midline before ascending to brain stem reticular formation

Does not cross midline

Crosses midline

Projects to and synapses with anterior colliculi, play major role in orientating eyes and head towards visual stimuli

The tract send fibers to grey matter with axons to post. horn of the spinal cord, can suppress incoming pain signal

Turck exam - Examines withdrawal reflex in spinal frog

Brondgest - facilitation and inhibition of the reflex

Sechenov - Component of the reflex arc

Turck exam - Relation between strength of the stimulus and response

Always consider left side symmetry

Consider central vs. peripheral deficits

Organize your thinking into seven categories

Organize your thinking into five categories