What is neurulation?
The development of the nervous system
How does the neural tube develop?
- Ectoderm of dorsal side is the neural plate
- Cells on the neural plate changes shape, plate folds onwards and forms a groove
- Separates from rest of ectoderm
- Neural tube extends and becomes spinal cord
How are neurons developed?
- Differentiation of neural tube in embryonic development
- Nervous system is formed
- Immature neurons migrate to final location
How do axons develop?
An axon grows from each immature neuron in response to chemical stimuli. Some extend beyond the neural tube to the body.
How do short axons work?
Form connections between Central nervous system
How do long axons grow?
Connect to any part of the body
How do synapses develop?
- developing neuron forms synapses
- synapses grow in between axons
- new synapses are formed throughout life with experience
- transmission across a synapse strengthens synapse
What is neural plasticity?
Synapses develop and are eliminated with experience in life. Highest plasticity up to age of 6. If not used, are eliminated (neural pruning) if used, transmission across a synapse strengthens the synapse.
What is spina bifida?
Incomplete closure of the neural tube
How does one accumulate spina bifida?
After neurulation, the centrum encloses and protects the spinal cord, as tissues from the centrum migrate around the neural meeting as an arch. In spina bifida, the arch is not properly fused
Where is spina bifida most common?
In the lower back
What do strokes cause?
Reorganisation of brain function in recovery to supplement damage
What happens in an ischemic stroke?
There is a disruption of blood to the brain, causing the brain to be deprived of oxygen and glucose, so cell respiration ceases in neurons and they irreparably are damaged and die
How is the brain developed?
The anterior part of the neural tube forms the brain in cephalization
What is the function of the medulla oblongata?
Autonomic control of the heart, gut muscles, breathing, blood vessels
What is the function of the cerebellum?
Coordination- eg unconscious functions like balance, posture
What is the function of the hypothalamus?
It is an interface between the brain and pituitary gland and synthesises hormones
What is the function of the pituitary gland?
Secreted hormones of the hypothalamus in posterior lobe and in anterior love produces hormones for body functions
What is the function of the cerebral hemispheres?
Interesting centre for complex functions, eg learning, memory, speech, emotion, reasoning, ordering, self awareness
What are different methods of brain research?
- lesion studies
- autopsy
- animal research
- MRI and fMRI to analyse pattern recognition and judgement of speed and movement
What is broca’s area?
A part of the left cerebral hemisphere associated with speech
What is the nucleus accumbens?
Pleasure and reward centre in each cerebral hemisphere which releases dopamine
What is the autonomic nervous system?
Centre of involuntary responses processed by the medulla oblongata. Comprises sympathetic and parasympathetic nervous system.
What do the parasympathetic and sympathetic nervous systems do?
They have contrary effects- parasympathetic increases actions, and processes body functions, sympathetic decreases body functions and is associated with survival processes
How does the pupil reflex show brain damage?
If light is shine in eye, pupil should constrict. The medulla controls this involuntary reaction so if it does not trigger the parasympathetic nervous system to cause circular muscle fibres to constrict, there is damage to the medulla.
What is the structure of the cerebral cortex?
- outer layer of cerebral hemispheres
- 2-4mm thick
- 6 layers of neurons
- enlarged with evolution- folding to fit in cranium
- left cerebral hemisphere receives input from sensory receptors on right side and vice versa
Why does the brain require a large amount of energy from respiration?
To maintain and re-establish resting potential and synthesise neurotransmitters
What are the different specialised receptors?
- mechanoreceptors
- chemoreceptors
- thermoreceptors
- photoreceptors
How do olfactory receptors work?
They are located in the epithelium of the upper nose, and odorant receptors are in the membrane. Volatile chemicals are smelled in nose and odorants from food in mouth can pass to nasal epithelium.
What do the cornea and lens do?
They focus light on to the retina
What do rods and cones do?
They are stimulated by light and detect the image focused on the retina and convert it to neural signals
How do Rods work?
They are sensitive and work well in dim light. Bright light causes the pigment to be temporarily bleached.
They cannot respond selectively to colours.
How do cones work?
There are 3 types which absorb different wavelengths: red, green and blue.
How do bipolar cells work?
They lead impulses from rods and cones to ganglion cells, acting as a synapse. If rods and cones are not stimulated, they depolarise and release an inhibitory neurotransmitter to bipolar cell which becomes hyperpolarised and don’t transmit to ganglion. When light is absorbed by rods and cones, rods and cones hyperpolarise and stops sending inhibitors to bipolar cells, which depolarise, activating adjacent ganglion.
What do ganglion cells do?
Send an action potential along the auditory nerves to the brain
What is the middle ear?
An air filled chamber between the outer and inner ear.
What is the eardrum?
A flexible, thin, taut sheet that separates middle ear from outer
What do the oval and round windows do?
Separate the middle ear from inner ear
Which bones form a connection between the eardrum and oval window?
Hammer, anvil wne stirruo
What do the ossicles do?
Transmit vibrations from the eardrum to the oval window, amplifying the sound 20 fold as the oval has a small SA
What do sensory hairs of the cochlea doing?
They detect sounds. Vibrations of the oval window push cochlea fluid forwards, transmitting vibrations to cochlea. Activation of different hairs distinguishes pitch and vibrations depolarise hair cells, which release neurotransmitters triggering an action potential along the auditory nerve.