Brainstem. Steven McLoon Department of Neuroscience University of Minnesota

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1 Brainstem Steven McLoon Department of Neuroscience University of Minnesota 1

2 Course News Change in Lab Sequence Week of Oct 2 Lab 5 Week of Oct 9 Lab 4 2

3 Goal Today Know the regions of the brainstem. Know major landmarks of each region and be able to identify each region in cross section. Understand the continuity of axon tracts from region to region. 3

4 Brainstem Geography Brainstem includes the medulla, pons and midbrain. All regions are visible on the side of the brain. 4

5 Brainstem Geography Not much of the brainstem is visible in a posterior view of the brain unless the forebrain and cerebellum are removed. 5

6 Brainstem Geography The cerebellum covers the IV ventricle on the surface of the brainstem. 6

7 Brainstem Geography The IV ventricle spans the entire pons and upper half of the medulla. 7

8 Brainstem Geography The presence of the ventricle is used to distinguish upper and lower medulla. 8

9 Spinal Cord Review Tracts of ascending axons carrying sensory information: Spinocerebellar tracts carrying proprioception Dorsal columns carrying proprioception and deep touch (uncrossed) Spinothalamic tract carrying pain, temperature and light touch (crossed) 9

10 Lower Medulla Dorsal columns and column nuclei 10

11 Somatosensory Pathway: Dorsal Columns for Proprioception and Touch The column axons synapse in nucleus gracilis and cuneatus. The axons of these neurons cross the midline and form the medial lemniscus to thalamus. 11

12 Lower Medulla Axons in the spinothalamic and spinocerebellar tracts continue up through the medulla. 12

13 Lower Medulla Pyramids are axons carrying motor information descending from cortex. 13

14 Lower Medulla 90% of the axons in the pyramids cross in lower medullar forming the lateral corticospinal tract. 10% remain as the anterior corticospinal tract. 14

15 Spinal Cord Review Tracts of descending axons carrying motor information from cortex: Lateral corticospinal tract (crossed) Anterior corticospinal tract (uncrossed) 15

16 Lower Medulla Cranial nerves III XII are attached to the brainstem. All have nuclei (sensory and/or motor) in the brainstem. 16

17 Upper Medulla IV ventricle (covered by cerebellum) choroid plexus openings into the subarchnoid space 17

18 Upper Medulla Pyramids 18

19 Upper Medulla Olive (external) and inferior olivary nucleus (internal) 19

20 Pons Basal pons with pontine nuclei 20

21 Pons Superior, middle and inferior cerebellar peduncles 21

22 Pons Superior, middle and inferior cerebellar peduncles Ventral surface of the cerebellum 22

23 Pons Corticopontine axons synapse in pontine nuclei Neurons in pontine nuclei send their axons to the cerebellum via the middle cerebellar peduncle 23

24 Spinocerebellar Pathway Spinocerebellar tracts enter cerebellum via inferior and superior cerebellar peduncles. 24

25 Pons Corticospinal, corticopontine and corticobulbar tracts (motor) pass through pontine nuclei. 25

26 Midbrain Cerebral peduncles (corticospinal, corticopontine, corticobubar tracts - motor) 26

27 Midbrain (lower) Inferior colliculus (auditory) 27

28 Midbrain (lower) Decussation of the superior cerebellar peduncles 28

29 Midbrain (upper) Superior colliculus (vision) 29

30 Midbrain (upper) Red nucleus related to the cerebellum and the motor system 30

31 Midbrain (upper) Substantia nigra sends axons to the basal ganglia; neurotranmitter is dopamine; degenerates in Parkinson s disease 31

Somatosensory Projection to Cortex Spinothalamic projection: Primary sensory axons for pain, temperature and light touch synapse on neurons in the horn.

32 Somatosensory Projection to Cortex Spinothalamic projection: Primary sensory axons for pain, temperature and light touch synapse on neurons in the horn. Axons of these horn neurons cross the spinal cord and ascend in the spinothalamic tract. They synapse in the posterolateral nucleus (VPL) of the thalamus. Axons from the VPL neurons project to somatosensory cortex. 32

Somatosensory Projection to Cortex Dorsal column projection: Primary sensory axons for proprioception and touch enter the horn and ascend in the columns.

33 Somatosensory Projection to Cortex Dorsal column projection: Primary sensory axons for proprioception and touch enter the horn and ascend in the columns. These axons synapse in nucleus gracilis (from lower body) and nucleus cuneatus (from upper body) in the medulla. Axons from these nuclei cross the medulla and ascend to thalamus. They synapse in the posterolateral nucleus (VPL) of the thalamus. Axons from the VPL neurons project to somatosensory cortex. 33

34 Somatosensory Pathway: Dorsal Columns for Proprioception and Touch Medial lemniscus ascends through the brainstem to thalamus. 34

35 Somatosensory Pathway: Spinothalamic Tract for Pain, Temperature & Touch Spinothalamic tract ascends through the brainstem to thalamus. 35

36 Motor System Axons of upper motor neurons descend from cortex. 36

General Sensory Pathways of the Trunk and Limbs

General Sensory Pathways of the Trunk and Limbs Lecture Objectives Describe gracile and cuneate tracts and pathways for conscious proprioception, touch, pressure and vibration from the limbs and trunk.