Introduction to brain anatomy Flashcards
What is the phenomenon of convergence?
When many pre-synaptic neurons converge on a single post-synaptic neuron
- average neuron receives 10,000 different inputs from synapses on it
- > a single cell receives multiple signals
What is the phenomenon of divergence?
Ability of a single cell to project on multiple cells
- axons of most pre-synpatic neurons divide into many branches that diverge to end on many post-synaptic neurons
- approx. 1,000 different axon terminals from one single neuron
- > a single cell sends multiple signals
What is the result of convergence and divergence?
Neural networks
- there are multiple ways of getting from one cell to another
- different cells will be excited according to the route chosen
- > different neural consequences
What is the general organisation of the Nervous System?
Central Nervous System (CNS)
> Brain
> Spinal Cord
Peripheral Nervous System (PNS) > Somatic (which we are conscious of) - Sensory - Motor > Autonomic (which we are not aware of) - Parasympathetic - Sympathetic
What are the components of the autonomic nervous system?
Parasympathetic Nerves > Cranial nerves - constrict pupils - stimulate saliva - slow heartbeat - constrict airways - inhibit release of glucose ; stimulate gallbladder > Sacral nerves - contract blader - promote erection of genitals
Sympathetic nerves > Thoracic nerves - dilate pupils - inhibit salivation - increase heartbeat - relax airways - stimulate release of glucose ; inhibit gallbladder - secrete epinephrine and norepinephrine > Lumbar nerves - relax bladder - promote ejaculation and vaginal contraction
How do the parasympathetic and sympathetic nervous systems work?
> They work in opposite ways
- e.g. PaNS constricts pupils vs. SyNS dilates pupils
> Although they send peripheral branches, they’re not restricted to the periphery alone
- in the brain, there are pathways wholly concerned with parasympathetic and sympathetic function
How do you differentiate neurons from the CNS and the PNS?
- If a neuron is entirely contained within the brain and/or spinal cord -> CNS neuron
- If any part of a neuron (dendrites, axon or cell body) projects outside of these structures -> PNS neuron
What are the anatomical compartments of the CNS?
> Forebrain
> Midbrain
> Hindbrain
- Pons
- Cerebellum
- Medulla
> Spinal cord
Why are spinal nerves “mixed” nerves?
They are composed of: > Receptors > Sensory neurons (dorsal input) - dorsal root ganglia -> dorsal root > Interneuron > Motor neuron (ventral output) > Muscle (receives information)
What are the divisions of spinal nerves?
Through which component do these nerves leave the spinal canal?
31 spinal nerves
- Cervical nerves (C1 -> C8)
- Thoracic nerves (T1 -> T12)
- Lumbar nerves (L1 -> L5)
- Sacral nerves (S1 -> S5)
- Coccygeal nerve (1)
All leave through intervertebral foramen
Where does the spinal cord end? What happens consequently?
Spinal cord ends at vertebral L1-L2 (lumbar division)
- > any nerve below L1 and L2 has to travel down until it finds its corresponding intervertebral foramen and exits
- > Cauda equina (horse’s tail): a group of nerves (S1 to Coccygeal nerve) at the base of spinal cord where there’s neural tissue (cell bodies) involved
Why is the cauda equina clinically important?
A needle can be inserted below L1 and L2 - e.g. to drain cerebral spinal fluid diagnostically, or if there’s a build up pressure - knowing you’re going below the spinal cord itself and therefore won’t damage it
e.g. lumbar punctures
What is the medulla and what is its function?
> Medulla is the oldest part of the hindbrain
Oldest part of the brain
Controls life-supporting centres
-> keeps you alive on a minute-to-minute basis
What are the components of the brainstem?
Midbrain and hindbrain
What is the role of the midbrain?
Relays information between the forebrain (above) and the hindbrain (below).
What is the role of the thalamus, regarding the nervous system?
Relays ascending and descending motor information.
What are the brainstem functions?
Brainstem = hindbrain + midbrain
> Conduit for ascending and descending pathways
> Conduit for cerebellar connections
> Houses most cranial nerve nuclei (12 pairs)
> Chemoreception, salivation, mastication, swallowing, gag reflex
> Reticular formation: arousal (i.e. wakefulness)
> Cardiovascular and respiratory centres: vital life-supporting role
> Raphe (serotoninergic pathways), locus nuclei (adrenergic pathways): mood, sleep
> Substantia nigra (dopamine - nigrostriatal pathway): movement control
What is Parkinson’s disease in terms of neurons?
Loss of dopamine neurons from one part of the substantia nigra
What is the role of the gyri (sing. gyrus) and sulci (sing. sulcus) of the cerebral cortex?
Increase the surface area of the brain to approx. 2,500 cm2
AND allows much more neural material to be contained within the skull
What does ‘nuclei’ refer to in neuroanatomy?
Refers to groups of cell bodies of similar function
vs. in genetics, the nuclei of cells containing genetic material
What are the 3 categories of cortical connections?
> Ascending (sensory) connections
Descending (motor) connections
Connections within the cerebral cortex
What are the various types of ascending cortical connections?
> Somatosensory, from thalamus (from spinal cord via thalamic nuclei)
Auditory, from thalamus (from cochlea via thalamic nuclei)
Visual, from thalamus (from retina via thalamic nuclei)
Smell, direct into olfactory cortex
Taste, from thalamus (from taste buds via thalamic nuclei)
-> Sensory information enters from spinal cord, and is transferred via the thalamus to various parts of the cortex, except for smell
What are the various types of descending cortical connections?
> Motor to the spinal cord (corticospinal tract)
Motor to the brainstem motor nuclei (corticobulbar tract)
Motor to the motor control centres (targeted to the basal ganglia and cerebellum)
To the limbic system
What are the various types of cortical connections within the cerebral cortex?
> On same hemisphere: association fibres connecting different brain regions
- e.g. between auditory and visual cortex -> visual + auditory info. -> better identification of what you’re eating
> On opposite hemispheres: commissural fibres (commissures)
- including the corpus callosum
What are projection neurons and fibres?
> Projection neurons that extend long distances, frequently connect structures from the brain to the spinal cord and vice versa
> Projection fibres: main pathway for major ascending and descending axons
-> motor and somatosensory fibres
What is Diffusion Tensor Tractography (DTI)?
What is its use?
> A type of MRI
- we look at ways water diffuses through structures
Particularly useful in imaging myeline
-> Plot individual pathways
-> Build a pattern of tracks within the brain
How is computer-enhanced Diffusion Tensor Tractography (DTI) used?
Used in surgical planning and in understanding how parts of the brain communicate between each other.
