Download The Brain The brain is responsible for everything we think, feel and

The Brain
The brain is responsible for everything we think, feel and do. The average adult brain weighs about
1.5kg. It is the largest organ in the human body.
The brain is made up of billions of neurons and has trillions of connections between neurons. These
connections create pathways that enable the transmission of information throughout the brain.
The brain has different parts and structures within it. The most important part of the brain is the
cerebral cortex.
Cerebral Cortex: the convoluted, wrinkled outer layer of the brain that is involved with information
processing activities.
The cerebral cortex is 2-4mm thick and when unravelled, it would cover about two A3 sheets of
paper.
The major roles or functions of the cerebral cortex include: perception, language, learning, memory,
thinking, problem solving, planning and the control of voluntary movements.
The cerebral cortex is divided into two halves. These halves are known as cerebral hemispheres.
Cerebral Hemispheres: two almost-symmetrical halves of the brain, known as the left and right
cerebral hemispheres, separated and connected by the corpus callosum.
Corpus Callosum: a band of nerve fibres that connects the left and right cerebral hemispheres
enabling the exchange of information and coordination of their activities.
Roles of the four lobes of the cerebral cortex in the control of motor,
somatosensory, visual and auditory processing in humans; primary cortex
and association areas.
FOUR LOBES OF THE CEREBRAL CORTEX
The cerebral cortex is divided into two hemispheres. Each of the hemispheres is further divided into
four areas known as cortical lobes. Each lobe has specialised functions.
Frontal Lobe: the largest of the four lobes, which occupies the upper forward half of each
hemisphere and is involved in higher mental abilities.
The frontal lobes are involved with attention, personality, the control of emotions and expression of
emotional behaviour.
The frontal lobe has two important specialised areas: the primary motor cortex and Broca’s Area.
1
Primary motor cortex: specifically involved in controlling voluntary bodily movements through its
control of skeletal muscles.
The primary motor cortex in the left frontal lobe controls voluntary movement of the right side of
the body.
The primary motor cortex in the right frontal lobe controls voluntary movement of the left side of
the body.
Each part of the primary motor cortex is devoted to a specific part of the body. The amount of the
primary motor cortex devoted to a particular body part corresponds to the complexity of its
movements. Hands and fingers take up a larger area of cortex as they control fine movements,
whereas the shoulder has a smaller area of cortex as it has a limited range of motion.
Broca’s Area: a specialised area of the brain located in the left frontal lobe that coordinates
movements of muscles involved in speech production and supplies this information to the
appropriate motor cortex areas.
Broca’s Area is located next to the primary motor cortex. It is positioned next to the area of the
primary motor cortex that is devoted to the lips, tongue and jaw. Broca’s area sends messages to the
primary motor cortex to initiate movement in the lips, tongue, jaw and vocal cords when reading
aloud or speaking.
Broca’s area is also involved with the meaning of words and the structure of sentences.
Parietal Lobe: receives and processes sensory information from the body and other sensory areas
in the brain; also involved in spatial perception and memory.
The parietal lobe allows us to process and perceive the sensations of touch, temperature, pressure
and pain. These sensations are processed in the somatosensory cortex.
Somatosensory cortex: a strip of neural tissue in each of the parietal lobes that receives and
processes information from the skin and body enabling perception of bodily sensations and
information about muscle movement and position of limbs.
The somatosensory cortex runs parallel to the primary motor cortex and like it has different parts
the body associated with areas of the cortex. Some body parts have a larger area of cortex devoted
to them, depending on the sensitivity of the body part. The hands and mouth have a larger area of
cortex as they are both sensitive areas and are constantly in use.
2
Temporal Lobe: primarily involved with hearing, but also plays an important role in memory, facial
recognition and the identification of objects.
The temporal lobe processes all sounds, either verbal or non-verbal. It is also involved in many
memory storage and retrieval tasks. Memories for facts, procedures, and personal experiences are
all processed and stored in the temporal lobes. Object identification and facial recognition also occur
in the temporal lobe.
The temporal lobe has two specialised areas: the primary auditory cortex and Wernicke’s Area.
Primary Auditory Cortex: an area in each of the temporal lobes that receives and processes sounds
from the ears.
Verbal sounds (words) are mainly processed in the left temporal lobe and non-verbal sounds are
processed in the right temporal lobe.
Wernicke’s Area: a specialised area in the left temporal lobe that is involved with comprehending
the sounds of human speech.
Wernicke’s area is located next to the primary auditory cortex.
Wernicke’s area plays a crucial role in interpreting human speech: understanding the spoken word
and making sense to others when speaking.
Occipital Lobe: receives and processes visual information.
Located at the base of each occipital lobe is the primary visual cortex. It is here that the majority of
visual information from the eyes is processed.
Primary Visual Cortex: a specialised area in the occipital lobes that receives and processes visual
information from the eyes.
Neurons within the primary visual cortex and other areas of the occipital lobe are specialised to
respond to different features of a visual stimulus such as shape, colour, motion and edges.
Association Areas
Aside from the specialised areas of each lobe of the brain, there are also association areas in each
lobe. These areas integrate sensory and motor information as well as other information from other
structures within the brain.
Association Area: an area of the cerebral cortex where information from different brain areas is
combined and integrated to perform more complex functions such thinking, learning and
remembering.
3
Hemispheric specialisation: the cognitive and behavioural functions of the
right and left hemispheres of the cerebral cortex, non-verbal versus verbal
and analytical functions.
Left Hemisphere
- Verbal
- Controls right side of the body
- Analysis: maths, sequential tasks, evaluation
- Logical reasoning
Right Hemisphere
- Non-verbal
- Controls left side of body
- Spatial and visual thinking: jigsaws, maps
- Creativity
- Fantasy (daydreaming)
- Art/music appreciation
- Recognising emotions
The role of the reticular activating system in selective attention and
wakefulness; role of the thalamus in directing attention and switching
sensory input on and off.
RETICULAR ACTIVATING SYSTEM
-
RAS is part of the reticular formation in the brain stem.
Reticular means network – looks like white netting or lace.
RAS is a network of neurons that extends into the brain and down into the spinal cord.
RAS controls the level of ‘alertness’ (awake, asleep, drowsy or somewhere in between)
Moruzzi and Magoun experiments on cats.
- ESB of RF on sleeping cats – woke them instantly
- Severed RF from brain – coma until death
RAS influences attention – can choose what we attend to (selective attention).
RAS highlights important information and arouses specific cortical areas. EG sleepy driver – kangaroo
– RAS – snap to attention
Two different sensory sources – RAS decides which is more important and directs our attention to it.
4
THALAMUS
Located in the mid-brain. If you stick your fingers in your ears until they touch – that’s where the
thalamus is.
3cm in length, looks like two footballs (ovids), one per hemisphere.
Thalamus is a relay station. It filters all sensory information, except smell, and transmits it to the
relevant area of the cerebral cortex.
Information from RF goes to thalamus to assist in level of alertness and wakefulness.
Injury to thalamus
= loss of senses. EG blindness, deafness, except smell.
= loss of arousal – lethargy through to coma.
Thalamus further filters information to direct our attention.
LaBerge and Buschbaum – letters test
Thalamus closes off pathways of incoming sensations during sleep to allow the brain to rest.
SPINAL CORD
Neurons – parts of the neuron (dendrites, axons, soma, myelin sheath, axon terminals, synapse)
Three types of neurons: motor neurons, sensory neurons and interneurons
Motor neurons – carry motor messages from the brain to the muscles of the body to enable
movement
Sensory neurons – carry sensory messages from the body to the brain
Interneurons – found in the brain and spinal cord, they receive sensory messages and transport
them to the brain and take motor messages from the brain and pass them back to the body.
S – sensory neurons
A – afferent
M – motor neurons
E – efferent
Sections of the spinal cord – 4 sections that correspond to different parts of the body.
Cervical, thoracic, lumbar and sacral.
If the spinal cord is severed, paralysis results in the body below the break in the spinal cord.
5
Contribution of studies to the investigation of cognitive processes of the brain
and implications for the understanding of consciousness including:
– studies of aphasia including Broca’s aphasia and Wernicke’s aphasia
– spatial neglect caused by stroke or brain injury
STUDIES OF COGNITIVE PROCESSES
Aphasia: a language disorder apparent in speech, writing or reading produced by an injury to brain
regions specialised in these functions.
Broca’s aphasia: a language disorder that affects the production of speech, consisting of very short
sentences comprising mostly nouns and verbs.
Wernicke’s aphasia: a speech impairment involving difficulties with speech comprehension and in
producing fluent speech.
Spatial neglect: an attentional disorder in which individual’s fail to notice anything on either their
left or right side.
Spatial neglect is a result of damage to the parietal lobe, most commonly in the right hemisphere.
People with spatial neglect behave as if one side of their world does not exist.
Split-brain – student activity
Youtube – Mike Gazzaniga and Alan Alda
6