Sensory Passway.ppt

Sensory pathways 1. Sensory systems allow us to detect, analyze and respond to our environment 2. “ascending pathways”

3. Carry information from sensory receptors to the brain 4. Conscious: reach cerebral cortex 5. Unconscious: do not reach cerebral cortex

6. Sensations from body reach the opposite side of the brain

Sensory pathways Types of Sensory receptors 1. 2. 3. 4. 5.

Free nerve endings (pain, temperature) (A) Pacinian corpuscle (pressure) (B) Tactile ( Meissner’s) corpuscle (touch) (C) Muscle spindle (stretch) (D) Bulbous (Ruffini) corpuscle (fine touch) (E)

A

B

E

D

C

Sensory pathways Somatic sensory pathways: 3 neurons • 1st neurons: located in the dorsal root ganglion of spinal nerves or in the peripheral ganglia of cranial nerves, central processes enter the spinal cord or brain stem; peripheral processes are distributed to the skin, mucous and muscles

vestibular ganglion

Sensory pathways Somatic sensory pathways: 3 neurons • 2nd neurons: located in the posterior horn of the spinal cord or sensory nuclei of brain stem, axons cross over (decussates) and ascend in spinal cord or brain stem to thalamus

① ② ③ ④

① Posteromarginal nucleus ② Substantia gelatinosa ③ Nucleus proprius ④ Nucleus thoracicus (nucleus dorsalis of Clarke)

Sensory pathways Somatic sensory pathways: 3 neurons • 3rd neurons: located in the thalamus and axons project to somatosensory cortex ① the ventral posterior (VPM &VPL)

-Receive fibers of general sensation) ② the medial geniculate body

- Receive fibers of hearing

③ the lateral geniculate body - Receive fibers of vision

Sensory pathways 1. Superficial sensory pathways of trunk and limb

① Lateral spinothalamic tract • Transmits Pain & Temperature Sensation • Receptor: Free nerve endings of the trunk and limb

① Lateral spinothalamic tract • Ist Neuron: Dorsal Root Ganglion

spinothalamic tract

(Pseudounipolar neurons) – Dorsal root of spinal nerves – Lissauer's tract

decussation

• 2nd Neuron: Dorsal Horn (substantia gelatinosa - Lamina I, II )

anterior white commissure

– Crossing - Spinothalamic Tract (spinal cord) - Spinal Lemniscus (brain stem) • 3rd Neuron: Thalamus (VPL) –

posterior limb of the Internal Capsule

• Lissauer's tract

posterior root Run upward 1-2 segments Dorsal Root Ganglion

Sensory pathways--Spinothalamic pathway ① Lateral spinothalamic tract • Termination: – primary somatosensory cortex (Brodmann's Areas 3, 1, and 2) (Midddle part of the postocentral gyrus, and the posterior part of the paracentral lobule • Lesion – contralateral loss of pain and temperature sensation below the level of lesion

Sensory pathways--Spinothalamic pathway ② Anterior spinothalamic tract • Transmits crude touch and pressure. • Receptor: tactile corpuscle and Pacinian corpuscle

Sensory pathways--Spinothalamic pathway ② Anterior spinothalamic tract

spinothalamic tract

• Ist Neuron: Dorsal Root Ganglion ( Pseudounipolar neurons) – Dorsal root of spinal nerves

decussation

– Lissauer's tract • 2nd Neuron: Dorsal Horn (nucleus proprius,

Lamina V ) – Crossing - Spinothalamic Tract (spinal cord) - Spinal Lemniscus (brain stem)

• 3rd Neuron: Thalamus (VPL) –

posterior limb of the Internal Capsule

anterior white commissure • Lissauer's tract

posterior root Run upward 1-2 segments Dorsal Root Ganglion

Sensory pathways--Spinothalamic pathway

Sensory pathways - Deep pathway 2. Deep sensory pathways of trunk and limbs ① Conscious deep sensory pathways – Receptor: proprioceptive receptors of muscles, tendon, periosteum and joint – Transmits fine touch and proprioception of the trunk and limbs.

• Fine touch • Two-Point Discrimination

Sensory pathways - Deep pathway ①Conscious deep sensory pathways – Ist Neuron: Dorsal Root Ganglion •

Dorsal root of spinal nerves

•

Ascending fibers ( gracile and cuneate fascilucus )

– 2nd Neuron: gracile nucleus, cuneate nucleus • Crossing - medial lemniscus – 3rd Neuron: Thalamus (VPL) • posterior limb of the internal capsule

Sensory pathways - Deep pathway ① Conscious deep sensory pathways – Termination: primary somatosensory cortex (Brodmann's Areas 3, 1, and 2)(superior and midddle part of the postocentral gyrus,

and the posterior Part of the paracentral lobule)

Sensory pathways - Deep pathway

Sensory pathways - Deep pathway

Arrangement of sensory projections

dorsal cloumn pathway

Sensory pathways - Deep pathway Dorsal column lesion dorsal column pathway

Left spinal cord injury

• Sensory ataxia Loss of sense of: •touch •proprioception •vibration in left leg

– Patient staggers; cannot perceive position or movement of legs – Visual clues help movement

Sensory pathways - Deep pathway ②Unconscious deep sensory pathways •

Receptor: receptors of muscles, tendon, periosteum and joint

•

Ist Neuron: Dorsal Root Ganglion

– Dorsal root of spinal nerves – Ascending fibers of gracile and cuneate fascilucus) – 2nd Neuron: thoracic nucleus • spinocerebellar tract • Superior and inferior cerebellar peduncles

Sensory pathways - Deep pathway 2. Unconscious deep sensory pathways • Termination: paleocerebelleum • sensory maps : – the vermis receives fibres from the trunk and proximal portions of limbs – the intermediate parts of the hemispheres receive fibres from the distal portions of limbs.

Sensory pathways - Deep pathway

Sensory pathways - Deep pathway Spinocerebellar tract damage • Cerebellar ataxia

– a neurological sign consisting of lack of voluntary coordination of muscle movements as in walking – It is caused by the lesion of the cerebellum. – Symptoms include: • Clumsy movements • Incoordination of the limbs (intention tremor) • Wide-based, reeling gait (ataxia)

Sensory pathways - Trigeminothalamic pathway 2. Sensory pathways of the head and face • Trigeminothalamic tract • Receptor: superficial receptors in the skin and mucosa, and Meissner's corpuscles and Pacinian corpuscles of the head and face • Receives input from trigeminal nerve, facial nerve, glossopharyngeal nerve and vagus nerve. • Transmits Pain, Temperature and crude touch, pressure and

tactile discrimination sensation from the face, head and neck.

Sensory pathways - Trigeminothalamic pathway • Ist Neuron: Trigeminal Ganglion • Trigeminal nerves • 2nd Neuron: • spinal nucleus of V (Pain & Temperature ) • pontine nuclei of V (tactile and pressure) • Crossing -Trigeminal Lemniscus • 3rd Neuron: • Thalamus (VPM) • posterior limb of the Internal Capsule

Sensory pathways - Trigeminothalamic pathway Trigeminothalamic tract •Termination: primary somatosensory cortex (inferior part of the postocentral gyrus)

Sensory pathways -summary

Sensory pathways – Visual pathway • Receptor: photoreceptors (rod and cone cells) • Ist Neuron: bipolar cells in the retina • 2nd Neuron: ganglion cells – Optic nerves – Optic chiasm – Optic tract

Sensory pathways – Visual pathway • 3rd Neuron: lateral genicular body – Optic radiation – posterior limb of the internal capsule • Termination: primary visual cortex (around calcarine sulcus)

Sensory pathways – Visual pathway

Sensory pathways – Visual pathway The visual pathway: The photoreceptors (rods and cones) → the bipolar cells (the first order neurons) → the ganglion cells (the second neurons) → optic nerve → the optic chiasma (fibers from the nasal halves of the retinae cross)→ the optic tract→ Within the chiasma a partial decussation → the lateral geniculate nucleus → the optic radiation (geniculocalcarine tract)→ around the calcarine sulcus of the occipital lobe

Sensory pathways – Visual pathway Neurons for pupillary light reflex • Neuron 1 • the photosensitive retinal ganglion cells convey information to the optic nerve . • The optic nerve connects to the pretectal nucleus of the upper midbrain, bypassing the lateral geniculate nucleus and the primary visual cortex. • These "intrinsic photosensitive ganglion cells" are also referred to as "melanopsin-containing" cells, and they influence the circadian rhythms and the pupillary light reflex.

Sensory pathways – Visual pathway Neurons for pupillary light reflex • Neuron 2 • From the pretectal nucleus, axons connect to neurons in the EdingerWestphal nucleus, whose axons run along both the left and right oculomotor nerves. • Neuron 3 • Oculomotor nerve axons synapse on ciliary ganglion neurons. • The postganglionic axons innervate the ciliaris and sphinctor pupillae

Sensory pathways – Visual pathway • Visual fields (field of view) – field of view is everything that causes light to fall onto the retina. – The normal human visual field extends to approximately 60 degrees nasally (toward the nose, or inward) from the vertical meridian in each eye, to 100 degrees temporally (away from the nose, or outwards) from the vertical meridian, and approximately 60 degrees above and 75 below the horizontal meridian. – The macula (fovea ) corresponds to the central 13 degrees of the visual field.

Sensory pathways – Visual pathway Visual Field Deficits

Sensory pathways – auditory pathway • Receptor: spiral organ • Ist Neuron: bipolar cells in the cochlear ganglion – cochlear nerves

• 2nd Neuron: cochlear nuclei – Trapeziod body – Lateral lemniscus

Sensory pathways – auditory pathway • 3rd Neuron: medial genicular body – acoustic radiation – posterior limb of the internal capsule • Termination: primary audi tory cortex) (areas 41 and 42) (transverse temporal gyri)

Sensory pathways – auditory pathway The acoustic(auditory) pathway Receptors (spiral organ of Corti) → the bipolar cells in the spiral ganglion (the first order neurons) → the cochlear

nerve → the cochlear nuclei (the second neurons) → the lateral lemniscus (also receive the fibers from the ipsilateral superior olivary nucleus and the cochlear nuclei)

→ the medial geniculate body (the third neurons) → the acoustic radiation → the transverse temporal gyri .

Sensory pathways – auditory pathway

Sensory pathways – equilibrium pathway • Receptor: hair cells in Crista ampullaris, Macular utricli and Macular sacculi • Ist Neuron: bipolar cells in the vestibular ganglion

– vestibular nerves • 2nd Neuron: vestibular nuclei – Trapeziod body – Lateral lemniscus

Sensory pathways – equilibrium pathway • Axons join: ① medial longitudinal tract -control the movement of the eyes and neck ② vestibular spinal cord tract ③ entering cerebellum ④ connect the reticular formation of the brain stem ⑤ connect cortex

Sensory pathways –equilibrium pathway Disorders of Equilibrium and Hearing: Meniere’s Syndrome 

Meniere’s syndrome – 

is a disorder of the inner ear that can affect hearing and balance to a varying degree.



It is characterized by episodes of vertigo, low pitched tinnitus, and hearing loss.



The hearing loss has a fluctuating then permanent nature, meaning that it comes and goes, alternating between ears for some time, then becomes permanent with no return to normal function.



The equilibrium is greatly disturbed.



Excessive amounts of endolymph in the membranous labyrinth

Sensory pathways –equilibrium pathway Disorders of Equilibrium and Hearing: Meniere’s Syndrome

Normal

Meniere’s