Reflexes and Sensory Modalities in Human Physiology

Reflex

It is an involuntary, predictable motor response to a stimulus without conscious thought.

Reflex Arc

Where does a reflex occurs?

1. Receptor

2. Afferent Neuron (Sensory)

3. Integrating center

4. Efferent Neuron (Motor)

5. Effector

What are the 5 components of the reflex arc?

Receptor

Usually a dendrite of a neuron receiving the stimulus

Afferent neuron (sensory)

A neuron that has an action potential carrying the signal to the CNS.

Integrating center

Component of the reflex arc either in the brain or spinal cord

Efferent neuron (motor)

A neuron that has an action potential carrying a signal away from the CNS.

Effector

The structure causing the effect.

Skeletal muscle reflex

Example of somatic reflex

Gland, smooth or cardiac muscle reflex

Example of autonomic reflex

- Corneal / Conjunctival Reflex

- Blink Reflex

- Pupillary Reflexes

- Convergence Reflex

Four types of eye reflexes

Corneal/Conjunctival Reflex

Contraction of the orbicularis oculi muscle causes closure of the eyelid (blinking).

Blink Reflex

Blinking upon rapid passing of hand in front of subject's face.

- Light / Photopupillary reflex

- Accomodation reflex

- Pupillary skin reflex

Three types of pupillary reflexes

Light / Photopupillary Reflex

Reflex of the pupil in response to bright light or dim light

Constricted

In bright light, pupil is?

Dilated

In dim light, pupil is?

Accommodation

It is the ability of the eyes to focus on objects at different distances so as to produce a clear vision.

Dilate

Focusing on far objects cause the pupils to?

Normal size / constrict

Focusing on near objects cause the pupils to?

Pupillary Skin Reflex

Dilation of the pupil upon pinching the cheeks

Convergence Reflex

Reflexive movement of the eyes medially when we view close objects

- Eyeballs are PARALLEL to each other

- No convergence of eyeballs

Convergence reflex of eyes when viewing distant objects

- Eyeballs come close to each other at a point

- There is convergence (duling)

Convergence reflex of eyes when viewing near objects

- Patellar reflex

- Biceps reflex

- Triceps reflex

- Ankle jerk

- Wrist reflex

Five types of stretch reflexes

Patellar Reflex

The appropriate response is contraction of the quadriceps femoris which results in a knee jerk or patellar reflex.

Biceps Reflex

Contraction of biceps and flexion of the forearm.

Triceps Reflex

Extension of the elbow

Ankle Jerk

Flexion of the foot

Wrist Reflex

Flexion of the wrist

Sneezing Reflex

A protective reflex when the nasal mucosa gets irritated

Sternutation

Sneezing reflex is also known as?

Palmar Reflex

Closing of the hand or flexion of the fingers.

Palmar Grasp Reflex

Reflex in infants that involves closing of the hand

Abdominal Reflex

Reflex that draws in the abdominal wall

Pharyngeal Reflex

Reflex that induces vomiting

Gag Reflex

Pharyngeal reflex is also known as?

Plantar Reflex

Plantar flexion of the toes

Axon Reflex

Reddens the skin; production of a red flare

Babinski's reflex

Fanning out of toes with dorsal extension of the big toe.

Triple response of Lewis

Axon reflex is also known as?

Red line / spot -> Flaring -> Wheal

What happens during axon reflex?

Palatal reflex

Contraction of the palatal muscle, important for swallowing

Epigastric reflex

Drawing in of the skin of the epigastrium

Cremasteric reflex

Elevation of the testes during stroking of the inner thighs

Gluteal reflex

Contraction of the gluteal muscle which is observed by the movement of the skin overlying the muscles

Reciprocal inhibition

Stimulation of one muscle causes the inhibition of antagonistic muscle.

Sensation

Conscious or subconscious awareness of external or internal stimuli

Sensory modality

Each type of sensation felt is?

Dermis (few in hypodermis)

Receptors are found in?

- Exteroceptors

- Proprioceptors

- Enteroceptors

Three types of sensory receptors

Exteroceptors

Receptor stimulated by forces outside the body (e.g., somatic sensations - temperature, touch, pain)

Proprioceptors

Receptor stimulated by activities of the muscles and articulations

Enteroceptors

Receptor stimulated by substances or conditions within the viscera (internal organs)

- Touch

- Pressure

- Cold

- Heat

- Pain

Five types of receptors for the different senses

- Meissner's corpuscles

- Merkel's disks

- Free nerve endings around a hair follicle

Receptors for touch

Vater-Pacini corpuscles

Receptors for pressure

End-bulb of Krause

Receptors for cold temperature

Corpuscles of Ruffini

Receptors for heat

Free nerve endings

Receptors for pain

3

How many types of pain can an individual distinguish?

Adaptation

The loss of sensation due to frequent stimulation

Stereognosis

Appreciation (or recognition) of the form of three-dimensional objects by palpation without the aid of vision

Somatosensory area in the cerebrum

Stereognosis is determined by what area of the brain?

Pressure Sensation

Sensation located on the deeper tissue; longer lasting; with less intensity; has rapid adaptation.

Referred Pain

Occurs when activation of nociceptors in the viscera results in a perception of pain that is localized to the body surface

Deep, superficial

In referred pain, only _______ pain can be referred, not _______.