Neuroscience

Part 2 – The Brain

Facts about the human brain

Human brain weighs about 1400 grams (3 pounds), as compared to:Cow -- 425-458 gramsLion -- 240 gramsDog (beagle) – 72 gramsWalrus -- 1020–1126 gramsBottle-nosed dolphin – 1500–1600 gramsNewborn human – 350-400

Number of neurons?

Average number of neurons in the brain = 100 billion

Number of neurons in octopus brain = 300 million (from How Animals See, S. Sinclair, 1985)

Number of neurons in honey bee brain = 950,000 (from Menzel, R. and Giurfa, M., Cognitive architecture of a mini-brain: the honeybee, Trd.

Cog. Sci., 5:62-71, 2001.)

Human cortex compared to various animal species

Did you realize?

There are as many, or more, nerve cells in the human brain than there are stars in the Milky Way!

Three major parts of the brain1. The brainstem—the oldest region of the brain.

Basic to survival.

2. The limbic system—linked to memory, emotion and drives.

3. The cerebral cortex—highest level of brain development, the most complex functions occur there.

1. The Brainstem The oldest part (in terms of evolution) and

central core of the brain, beginning where the spinal cord swells as it enters the skull; the brainstem is responsible for automatic survival functions.

Brainstem (figure 5.5)

The Brainstem Medulla - the first large swelling at the top

of the spinal cord, forming the lowest part of the brain, which is responsible for life-sustaining functions such as breathing, swallowing, and heart rate.

Pons – (“bridge”) the larger swelling above the medulla that connects the top of the brain to the bottom and that plays a part in sleep, dreaming, left–right body coordination, and arousal.

The Brainstem Reticular formation (RF) - an area of neurons running

through the middle of the medulla and the pons and slightly beyond; it is responsible for selective attention. Also plays a role in arousal to help with alertness.

Cerebellum (“little brain”) - part of the lower brain located behind the pons that controls and coordinates involuntary, rapid, fine motor movement. Also coordinates voluntary movements involved in skills like walking, writing, playing an instrument, swimming, etc.

2. The Limbic System

A doughnut-shaped system of neural structures located under the cortex and above the brainstem.

Associated with learning, emotion, memory and motivation

Limbic system: Thalamus - part of the limbic system located in the

center of the brain, this structure relays sensory information from the lower part of the brain to the proper areas of the cortex and processes some sensory information before sending it to its proper area.

Hypothalamus - small structure in the brain located below the thalamus and directly above the pituitary gland. Directs maintenance activities, helps govern endocrine system, linked to emotion, part of reward system. Responsible for motivational behavior such as sleep, hunger, thirst, and sex.

Sits above and controls the pituitary gland (master endocrine gland).

Limbic system (continued)

Hippocampus - curved structure located within each temporal lobe, responsible for the formation of long-term memories and the storage of memory for location of objects.

Amygdala - brain structure located near the hippocampus, responsible for fear responses and memory of fear.

3. The Cerebral Cortex

The extensive outer layer of gray matter of the cerebral hemispheres, largely responsible for higher thought processes, and interpretation of sensory input.

Cerebral Hemispheres Cerebral hemispheres - the two sections of the cortex

on the left and right sides of the brain. Corpus callosum - thick band of neurons that

connects the right and left cerebral hemispheres.

Left Hemisphere: Controls the right hand, spoken language, written language, mathematical calculations, logical thought processes, analysis of detail, reading.

Right Hemisphere: Controls the left hand, nonverbal, visual-spatial perception, music/artistic processing, emotional thought & recognition, processes the whole, pattern & facial recognition.

Four lobes of the brain

Four Lobes of the Brain Occipital lobe - section of the brain located at the rear and

bottom of each cerebral hemisphere containing the visual centers of the brain. Primary visual cortex – processes visual information from

the eyes.

Parietal lobes - sections of the brain located at the top and back of each cerebral hemisphere containing the centers for touch, taste, and temperature sensations. Somatosensory cortex - area of neurons running down

the front of the parietal lobes responsible for processing information from the skin and internal body receptors for touch, temperature, body position, and possibly taste.

Four Lobes of the Brain

Frontal lobes - areas of the cortex located in the front and top of the brain, responsible for higher mental processes and decision making as well as the production of fluent speech. Motor cortex - section of the frontal lobe located at the back,

responsible for sending motor commands to the muscles of the somatic nervous system.

Temporal lobes - areas of the cortex located just behind the temples containing the neurons responsible for the sense of hearing and meaningful speech. Primary auditory cortex – processes auditory information

from the ears.

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Four lobes

Motor Cortex (controls)

An area at the rear of the frontal lobes that controls voluntary movements.

Certain areas of the motor cortex relate directly to different body parts. Left side controls the right side of body; right side controls the left side of body.

Somatosensory Cortex (receives input)

the area at the front of the parietal lobes that registers and processes body touch and movement sensations.

Certain areas of sensory cortex relate directly to different body parts. Left side receives information from the right side of body; Right side receives information from the left side of body.

Motor and somatosensory cortexes

Watch video on the phantom limb syndrome.

Visual Cortex—located in the back of the head in the occipital lobe.

Auditory cortex---located in the temporal lobe.

Association Areas Areas of the cerebral cortex that are not involved

in primary motor or sensory functions; rather, they are involved in higher mental functions such as learning, remembering, thinking and speaking.

Used to integrate information.

Plasticity

The brain’s capacity for modification, as evident in brain reorganization following damage and in experiments on the effects of experience on brain development.

Plasticity occurs in the brain under two primary conditions: 1. During normal brain development when the

immature brain first begins to process sensory information from childhood through adulthood.

2. As an adaptive mechanism to compensate for lost function and/or to maximize remaining functions in the event of brain injury.