ascending descending tracts

DR. ANEELA JAMIL

ASCENDING & DESCENDING TRACTS

SPINAL CORD TRACTS

• Sensory information (receptors) -> Brain by means of ascending tracts of fibres that conduct impulses up the spinal cord.

• Brain(motor activities in the form of nerve impulses) -> Spinal cord by means of descending tracts of fibres that travel down the spinal cord.

Tracts• bundles of axons in the white column

• Ascending tracts• carry information to brain

• Descending tracts• carry motor commands to spinal cord

SENSORY FIRST-ORDER NEURON

• For all sensory pathways, the cell body of a first-order sensory neuron is located in dorsal root ganglion or cranial nerve ganglion

SECOND-ORDER NEURON

• May be located in the spinal cord or brain stem

THIRD-ORDER NEURON

• Located in the thalamus

ASCENDING TRACTS

• Carry sensory information from the periphery to the spinal cord and up to the brain.

• Pathway consists of1. receptor cell -> spinal cord (or brain stem)2. spinal cord cell -> thalamus3. thalamus -> primary sensory cortex

Figure 15–4

ASCENDING TRACTS

• Dorsal column system• Anterolateral column system

POSTERIOR WHITE COLUMN PATHWAY

• Modalities Pressure,propioception,vibration• Ist order neuron Dorsal root ganglion• 2nd order neuron Medulla oblongata Medial

Leminiscus• 3rd order neuron Thalamus• Termination Postcentral gyrus

MEDIAL LEMINISCAL PATHWAYMEDIAL LEMINISCAL PATHWAY

Ipsilateral loss of sensationsIpsilateral loss of sensations below the level of lesionbelow the level of lesion

SPINOTHALAMIC TRACT

• Modalities Pain,temperature,itch,sexual

sensations, crude touch• Ist order neuron Dorsal root ganglion• 2nd order neuron Dorsal horn of spinal cord• 3rd order neuron Thalamus• Termination Postcentral gyrus

SPINOTHALAMIC TRACTSPINOTHALAMIC TRACT

ContralateralContralateral loss of loss of sensations sensations below below the the level of lesionlevel of lesion

MOTOR PATHWAYS

• Pyramidal Tract• Extrapyramidal tract

UMNL LMNL

• Type of Paralysis Type of Paralysis Spastic FlaccidSpastic Flaccid• Atrophy No Atrophy Atrophy No Atrophy

Severe Severe • Reflexes Reflexes HyperreflexiaHyperreflexia

HyporeflexiaHyporeflexia• Clonus Present Absent Clonus Present Absent

• Fasciculations Fasciculations Absent Absent

PresentPresent • Tone Tone Hypertonia Hypertonia

HypotoniaHypotonia

CORTICOSPINAL TRACT • Also called pyramidal tract• Provides voluntary control over skeletal

muscles

CORTICOSPINAL TRACT

EXTRAPYRAMIDAL MOTOR PATHWAYS

• Reticulospinal tract • Vestibulospinal tract • Tectospinal tract• Olivospinal tract • Rubrospinal tract

SPINAL CORD TRAUMAPARALYSIS

• Paralysis – loss of motor function Flaccid paralysis Spastic paralysis• Flaccid paralysis – damage to Lower

motor neurons• Spastic paralysis – damage to Upper

motor neurons

• Paraplegia - transection between T1 and L1, paralysis of lower limbs

• Quadriplegia - transection in the cervical region, paralysis of all limbs

• Monoplegia - paralysis of only one limb• Hemiplegia – paralysis of one half of the

body(left/right).

BROWN-SEQUARD SYNDROME (SPINAL CORD HEMISECTION)

Major Symptoms

1. ipsilateral loss of motor activity 2. ipsilateral loss of Dorsal column sensations below the level of lesion

3. contralateral loss of pain and temperature sensations below the level of lesion