slides on reflexes, DTR

Muscle spindle
• A small, complex spindle-shaped sensory receptor located in skeletal muscle
• senses muscle stretch
• consists of several modified muscle fibres, called intrafusal fibres

• The ends of these fibres are contractile
• central portion is non-contractile and innervated by special neurones/gamma motor neurones).
Basic reflexes:
The myotatic(stretch) reflex
The inverse myotatic reflex
The flexion withdrawal-crossed extensor reflex
Motor outputs
Involuntary
Stereotyped
Elicited by specific sensory inputs
The stretch reflex
Designed to maintain muscle length
-by countering a muscle stretch
-with a muscle contraction
Provides the basis for muscle tone
Also called deep tendon reflexes
-rapid, passive muscle stretch activates muscle spindles
-spindle afferents (oarticularly Ia) send impulses to the spinal cord
-connections to homonymous muscle alpha neurons: Monosynaptic
-connections to synergistic muscle alpha motor neurons; monosynaptic
--cause the stretched muscle to contract
Connection to the antagonist muscle thru inhibitory neuron—decreases activity of the antagonist muscle
Inverse myotatic reflex
Designed to control muscle tension
-by countering a muscle contraction with relaxation
-plus contraction of the antagonist mmuscle
Allows controlof muscle force

The flexion withdrawal and crossed extensor reflexs
Designed to withdraw one limb from a painful stimulus, while extending the cnotralateral limb for support

Reflexes ;window into the nervous system
- is sensory pathwayintact?
- -is motor output pathway intact?
deep tendon reflexes:

-present normally
-weak of absent with posterior root, LMN, or anterior root lesion,
-weak or absent with acute UMN lesion
-increased with chromic UMN lesion
Some DTRs often tested;
-biceps(C5-6)
-triceps(C7)
Patellar (knee jerk;L3-4)
-achilles (ankle jerk reflex;S1)

Superficial reflexes;
Present normally
-weak or absent with posterior root, LMN< or anterior root lesion,
-weak of absent with UMN lesion
-relfexes testet; abdominal and cremasteric

Plantar reflex
Present normally
Absent with posterior root, LMN, or anterior root lesion
With UMN lesion, plantar flexion is replaced by extensor plantar response(up-going-toes)
-called babinski reflex
Indicates damage to corticospinal tract
-a remnant nociceptive avoidance reflex

Clonus
-rythmic contractions and relaxations of amuslce grup
-often accompanies increased DTRs seen with UMN damage
bIceps brachii(C5)
=purpose – to provoke a root (C5) or cord(cns)sign
-positive response
-hypoactive (root)
Hyperactive (cord-cns)
Brachioradialis(c6)
Positiveresponse
-hypoactive- root
Hyperactive – cord- cns
Triceps (c7)
Hypoactive root
Hyperactive – cord –cns
Quadriceps(L4)
Hypoactive –root

Hyperactive—cord—cns
Gastroc-soleus(S1)
Hypoactive –root
Hyperactive—cord –cns
In general

reflexes are not pathological if symmetric unless they are absent or hyperreflexic

Assymetry of reflexes and absent reflexes tend to localize to a peripheral nervous system process
Increased reflexes tend to indicate a problem of the central nervous system
Reflexes are routinely tested on neuro exam and are nonspecific as to the etiology of the disease process if abnormal.

They provide information to help localize the problem

the pupillary reflex or pupillary light reflex

is the reduction of pupil size in response to light.

It is a normal response and dependent on the function of the optic nerves and oculomotor nerves
Lack of the pupillary reflex or an abnormal pupillary reflex
can be caused by
optic nerve damage
oculomotor nerve damage
brain death
and depressant drugs
such as barbiturates
The optic nerve is responsible for the afferent limb of the pupillary reflex, or in other words, senses the incoming light.

The oculomotor nerve is responsible for the efferent limb of the pupillary reflex; in other words, it drives the muscles that constrict the pupil.
Dependent on how the pupils constrict or do not constrict one can determine which of the cranial nerves is damaged.