Central Nervous System – the brain and spinal cord

“The brain is the body’s most important organ, but keep in mind it’s the brain that is telling you that.”

Brain is composed of 100 billion neurons plus supporting cells

Parts of the brain? (diagram)
Four main parts:
1. Brainstem – most primitive part: vital functions. Basic things
i. Pons and medulla oblongata
1. Responsible for heart rate, vasomotor tone, respiration,
2. Reticular formation – responsible for waking the cerebral cortex

2. Diencephalon

• Hypothalamus – homeostasis, thirst, hunger, controlling the pituitary gland (major hormone producer), etc
• Thalamus – sensory relay and editing
• Pineal gland -- produce melatonin for sleepiness

3. Cerebellum = coordinates movement

• Responsible for fine motor coordination, posture and balance

4. Cerebrum = thinking, process sensory info
i. most recently evolved part of the brain
ii. brain convoluted for more surface area
ß ridges/hills = gyrus
ß valley = sulcus
ß big central valley = central sulcus
∑ divides frontal and parietal lobes
∑ area behind (part of parietal lobe) for receiving sensory input = sensory strip
∑ in front of central sulcus (part of frontal lobe) is area designated for control of voluntary muscles = motor strip
ß big lateral valley = lateral sulcus
- divides temporal lobe from rest (frontal and parietal)
iii. outermost layer is the cerebral cortex (1-4 mm thick) made of gray matter containing 75% of the brain’s neurons - most thinking takes place here
iv. inner part = myelinated (white)

v. two hemispheres connected by the corpus callosum
vi. each hemisphere is divided into four lobes

1. frontal lobe – anterior to the central sulcus

• integrates muscle activity, speech (Broca’s area) and thought
• precentral gyrus = motor strip (Homunculus Model)
• designated for control of voluntary muscles

2. parietal lobe – behind the central sulcus
- receives and processes sensory information, and hearing
- postcentral gyrus = sensory strip
n receiving sensory input

3. temporal lobe – inferior to the lateral sulcus
- receives auditory signals, processes language

4. occipital lobe – behind the parietal lobe
- processes visual information

i. brain lateralization – each hemisphere exhibits functional specialization
- speech and language processing are in the left hemisphere
1. may be related to handedness – left brain dominant in right-handed individuals and vice versa (not consistent)
2. 2 hemispheres w/ opposite control:
ß Left controls and senses right side of body
ß Right controls and senses left side of body
o If stroke on L, paralyzed on R. some aspects only on one side ‡ speech (motor speech area = Broca’s area) Central sulcus

Note that the Homunculus Model shows the motor and sensory strips. The area of the brain that responds to parts of the body is not proportional since you need more sense and motor control of things like hands and lips…
If lose hand (blown off…) then area void of info. Info that creeps in is still interpreted as hand ‡ phantom limb syndrome


Communication with the brain and body:
Sensory impuse from skin receptor ‡ spinal cord ‡ medulla (crosses over) ‡ pons ‡ midbrain ‡ cerebrum ‡ sensory cortex of parietal lobe ‡motor cortex of frontal lobe ‡ cerebrum ‡ midbrain ‡ pons ‡ medulla (x-over) ‡ spinal cord ‡ motor neuron ‡ muscle