Pyramidal and extrapyramidal tracts

Pyramidal and extrapyramidal

tracts

• The low decerebrate human is usually comatose and shows extensor spasticity as in the later stages of spinal transection, but of more severity. – The low decerebrate animal cannot stand by itself

despite the heightened extensor tone, partly because it lacks vestibular control to maintain upright posture. • It cannot right itself if turned upside down; it cannot

walk; and it cannot regulate its temperature or endocrine function.

• In decorticate rigidity, the hypertonicity is usually unidirectional, predominantly in the anti-gravity muscles. Thus, in the upper limbs, extension is resisted, and in the lower limbs, flexion is resisted. clasp(pen)-knife

• Neck reflexes– Left-right– Up-down• Up – front flex, hind ext• Down – front ext, hind flex

• Labyrinthe reflexes - decerebrate– Dorsal position – extension– Ventral – flexion

• Labyrinthe reflexes - decorticate– Head righting

cerebellum

• three functional divisions, based on the principal sources of afferent fibres – mossy fiber– pontine nuclei (motor cortex)– spine– vestibular nuclei

• In addition, all parts of the cerebellum receive fibres from the contralateral inferior olivary complex of nuclei in the medulla – climbing fibers, learning

cerebellum

Spin

al c

ord

Motor cortex

Vestibular ncl

1. Vestibulocerebellum = nodule and the two flocculi = Archicerebellum = (Fastigial nucleus) = from the vestibular ganglion and nuclei = balance = vertigo, nystagmus and an unsteady gait.

2. Spinocerebellum = Paleocerebellum = Interposed nucleus = globose and emboliform nuclei = the vermis and adjacent cortex of the anterior lobe and of part of the posterior lobe = from spine = muscle tone = ataxia (alcohol)

3. Pontocerebellum = Neocerebellum = Dentate nucleus = cerebellar cortex = from the pontine nuclei (from motor cortex) = voluntary = ipsilateral ataxia

1 23

Basal ganglia (1)

• The basal ganglia are important to life nuclei in the brain interconnected with the cerebral cortex, thalamus and brainstem.

• Basal ganglia are associated with a variety of functions: motor control, cognition, emotions and learning.

• Parts: – the striatum (putamen, caudate nucleus, nucleus

accumbens)– globus pallidus (internal and external segments)– subthalamic nucleus (STN) – substantia nigra (SN) - compacta (SNc), reticulata (SNr)

• Red excitatory• Blue inhibitory• Magenta dopa

Parkinson's disease (2)

• Mnemonic device• T - Tremor - Involuntary trembling of the limbs

(resting tremor)• R - Rigidity - Stiffness of the muscles• A - Akinesia - Lack of movement or slowness in

initiating and maintaining movement• P - Postural instability - Characteristic bending or

flexion of the body, associated with difficulty in balance and disturbances in gait

Parkinson's disease (2)

Dopaminergic pathways of the human brain in normal condition (left) and Parkinson's disease (right).

Red Arrows indicate suppression of the target, blue arrows indicate stimulation of target structure.

chorea putamen

subst. Nigra

dopa

tremorakinesiarigidity

athetosiswrithing movementspallidum

hemibalismnc. subthalamicus