Structure and Function of a neuron:
1. What is the structure and function of a sensory
neuron:
● The sensory neuron carries messages from the
Peripheral Nervous System (PNS) to the Central
Nervous System (CNS).
● They have a long dendrite and short axon
2. What is the structure and function of a relay
neuron:
● The relay neuron connect sensory neurons to
other motor neurons and other relay neurons
● They have short dendrites and axons
3. What is the structure and function of a motor
neuron:
● The connect the CNS to effectors (muscles and glands)
● They have short dendrites and long axons
What is the structure of a neuron in general?
Cell body, or soma, contains a nucleus, which carries the genetic makeup of a cell. Branch-like structures,
called dendrites protrude outside the cell body and carry nerve impulses from the neighbouring cells towards
the cell body
The axon carries the impulse away from the cell body down the length of the neuron. It is covered in a fatty
layer/sheet, called myelin sheath, it speeds the process of transmission and protects the neuron.
● If the myelin sheath is CONTINUOUS, it would reverse the effects of transmission and slows down the
electrical impulse
● Therefore the layer is segmented into gaps, called nodes of Ranvier- which speeds up the process of
transmission as it forces the impulse to ‘jump across’ the neuron
Type of neuron Where is the neuron located
Sensory Located outside the CNS, in the PNS, in clusters called ganglia
Motor They may be in the CNS, but their long axons form part of the PNS
Relay Make up 97% of all neurons , most found in brain and visual systems
.
What is electrical transmission and how does it fire the neuron?
When a neuron is resting, the inside of the cell is (-) charged compared to the outside of the cell. When a
stimulus activates a neuron, for a split second, causes the inside of the cell to become (+) charged, thus
causing an action potential to occur, which allows the impulse to travel all the way down the neuron to the
axon.
, Localisation of Function A01 AND A03:
A01:
Task: Define each key term
Phineas Gage case
AREA FUNCTION
Localisation of Function The belief that different areas of the brain are responsible for specific behaviours,
processes or activities.
Motor Area A region of the frontal lobe that is involved in regulating movement
Somatosensory area An area of the parietal lobe that processes sensory info such as touch
Visual Area An area of the occipital lobe that receives and processes visual information
Auditory area Located in temporal lobe concerned with the analysis of speech based info
Broca’s area Located in frontal lobe on the left (most people), responsible for speech production
Wernicke's Area Located in temporal lobe (encircling the auditory cortex), in left hemisphere (in most
people), responsible for language comprehension
Summarise localisation VS Holistic theory:
★ Prior to Broca and Wernicke’s discovery, scientists supported the holistic theory, that all parts of the
brain were involved in thought and action processing
★ During the 19th century, Paul Broca and Karl Wernicke, found LOCALISED brain functions (cortical
specialisation), and believed that if one part of the brain was damaged, due to illness or injury,
functions associated with that part of the brain will also be affected.
Summarise hemispheres and lobes in the brain:
★ The brain is divided into two hemispheres, the left and right, each controlling functions on the opposite
side of the body. This lateralization extends to language, primarily linked to the left hemisphere
I.E- THE LEFT HEMISPHERE CONTROLS THE RIGHT SIDE OF THE BODY AND RIGHT HEMISPHERE
CONTROLS THE LEFT SIDE OF THE BODY.
★ The cerebral cortex, the outer layer of both hemispheres, contains four lobes: frontal, parietal,
occipital, and temporal.
★ The motor area in the frontal lobe governs voluntary movements on the opposite side of the body,
while the somatosensory area in the parietal lobe processes sensory information from the skin.
★ The occipital lobe's visual area interprets input from the eyes, and damage can result in specific
blindness. The temporal lobes, housing the auditory area, analyse speech-based information, and
damage may lead to hearing loss. Wernicke's area, located in the temporal lobe, plays a role in
language comprehension, and its impairment can impact language understanding.
, Summarise language centres in the brain and aphasia’s:
★ Language functions are primarily localised in the left hemisphere. In the 1860s, Paul Broca identified
Broca's area in the left frontal lobe, crucial for speech production.
★ Damage to this area results in Broca's aphasia, characterised by slow, laborious speech lacking
fluency. Broca's most famous patient, 'Tan,' could only utter the word "Tan."
★ Around the same time, Karl Wernicke identified Wernicke's area in the left temporal lobe, responsible
for language understanding.
★ Damage to Wernicke's area leads to Wernicke's aphasia, where individuals produce fluent but
meaningless speech. People with Wernicke's aphasia may use neologisms, creating nonsensical
words in their speech.
A03: Evaluation:
STRENGTH LIMITATION
One strength of localisation of function is that there One limitation is that language may not be localised
is research support from mental disorders. just to Broca's and Wernicke's areas.
Neurosurgery is seen as a last resort treatment for A recent review by Anthony Dick and Pascale
mental disorders, targeting specific areas of the Tremblay (201) found that only 2% of modern
brain. For example, cingulotomy involves isolating a researchers think that language in the brain is
brain region called the cingulate gyrus, which is completely controlled by Broca's and Wernicke's
implicated with OCD. Dougherty et al, reported that areas. Advances in brain imaging techniques, such
44 patients underwent this surgery, and after a 32 as fMRI, mean that neural processes in the brain
week post-surgery, 30% had a positive response to can be studied with more clarity than ever before. It
the surgery with 14% with partial response. This is a seems that language function is distributed far more
strength because the surgery suggests that there holistically in the brain than was first thought.
are localised functions of the brain with certain So-called language streams have been identified
disorders. across the cortex, including brain regions in the right
hemisphere, as well as subcortical regions such as
the thalamus.
This suggests that, rather than being confined to a
couple of key areas, language may be organised
more holistically in the brain,
Another strength of localisation of function is that A limitation of this comes from LASHLEY, who
there is research support from brain scans. studied rats removing 10-50% of the cortex, when
Petersen et al, used brain scans to demonstrate that they were learning the route of a maze.No area was
Wernicke's area was active during a listening task proven to be more important than any other area in
and that Broca’s area was active during a reading terms of the rats' ability to learn the route. The
task. Long term memory tasks were studied by process of learning seemed to require every part of
Buckner and Peterson, which showed semantic and the cortex rather than being confined to a particular
acoustic memories were located in the prefrontal area.
cortex. The objective methods, therefore, makes This suggests that higher cognitive processes, such
Peterson’s and Buckner’s work reliable, thus making as learning, are not localised but distributed in a
this a strength as it supports localisation of function. more holistic way in the brain.
