Functional Anatomy of the Brain Flashcards
FOREBRAIN
- Telencephalon and Diencephalon
- Brain structures; cerebrum, thalamus & hypothalamus
- Brain cavities; lateral ventricles & third ventricle
- Nerves; Olfactory (I) and Optic (II)
MIDBRAIN
- Mesencephalon
- Brain structures; midbrain
- Brain cavities; mesencephalic aqueduct
- Nerves; cranial nerve III & IV
HINDBRAIN
- Metencephalon & Mylencephalon
- Brain structures; Pons, Cerebellum & Medulla Oblongata
- Brain cavities; fourth ventricle
- Nerves; Trigeminal (V) & VI-XII
Gross anatomy divisions (7)
- Cerebrum
- Cerebellum
- Brainstem
- Pons
- Medulla Oblongata
- Midbrain
- Diencephalon
Cerebrum
Telencephalon
- the largest part of the brain
- carries higher functions
- two cerebral hemispheres separated by cerebral fissure
- Gyri (ridges) & Sulci (grooves)
- Grey matter; neuronal cell bodies
- Central white matter; axons and basal nuclei
- Receives input from sensory organs
- voluntary skeletal muscle movements, stores memory,
voluntary motor control, behaviour and mental status
Grey Matter
- Made up of neuron cell bodies
- Located on surface & deep in hemispheres; in hippocampus, basal and septal nuclei
Limbic system
Complex structures on both sides of the thalamus, ancient memory and emotional complex
White matter
Contains myelinated nerve fibres
- major neural connection between hemispheres (corpus callosum)
Types of white matter fibres
- association fibres
- commissural fibres
- projection fibres
Association fibres
interconnect adjacent gyri
establish connection within same hemisphere
Commissural fibres
Connects two hemispheres
Projection fibres
Connects cerebral cortex to other parts of the brain and spinal cord
Characteristics of the cerebral cortex
- acquired late in evolution
- cause consciousness
- 3x regions; motor cortex, sensory cortex and association cortex
3x regions of the cerebral cortex
- Motor cortex; responsible for non-reflex movement (contralateral)
- Sensory cortex; responsible for sensory perception
- Association cortex; complex memory, planning, self-awareness, language and personality traits
Lobes of the cerebrum
- Frontal lobe; part of motor cortex
- Occipital lobe; visual cortex
- Parietal lobe; conscious perception of pain, heat and touch
- Temporal lobe; auditory function, behaviour & memory
- Piriform; conscious olfaction
Brain stem
- Continuous with spinal chord
- diencephalon, medulla oblongata, midbrain & pons
Diencephalon
most rostral part of the brainstem
- divided into 4 regions; hypothalamus, thalamus, subthalamus and epithalamus
Thalamus
Large number of grey matter communicating with cerebral cortex
- all senses except smell come to the thalamus
- interprets awareness of nonlocalized pain, touch and temperature
- the optic nerves form the optic chiasm of the diencephalon
- Rostral to the optic chiasm, optic nerves (CN II) runs to the eyeball
Mesencephalon
- Divided into two sections; dorsal (tectum) and ventral
- 4 round swellings characterise tectum (corpa quadrigemina)
Pons
Between medulla oblongata and mesencephalon
- composed of dorsal part (tegmentum) and ventral
- connected to cerebellum via the cerebellar peduncles
- contains rostral end of fourth ventricle and gives rise to the trigeminal nerve.
Cerebellum structure
- transverse cerebral fissure separates it from cerebrum
- 3 cerebellar peduncles on each side of the 4th ventricle connects it to the brainstem
- grey matter is the external layer
- white matter; arbor vitae
Cerebellum function
- maintains balance
- motor reflex centre; muscle contractions
- Ipsilateral; motor effect exerted on the same side
Medulla Oblongata
- Gives rise to seven of the 12 cranial nerves
- grey matter nuclei, white matter tracts
- regulation of visceral functions; heart rate, respiration etc.
Meninges
Brain and spinal cord are enveloped by 3 layers of connective tissue; meninges
- Dura mater; thick outer layer
- Arachnoid layer; thin middle layer, non-vascular
- Pia mater; inner vascular layer, firmly attached to underlying nervous tissue
Subarachnoid space
Space between the pia mater and the arachnoid layer
- filled with CSF cerebrospinal fluid
Ventricles
Derived from the fluid-filled centre of the embryonic neural tube
- interconnected cavities filled with CSF
- 4 ventricles connected to each other and the central canal in the spinal cord
The ventricular system
- the two most rostral ventricles are called lateral ventricles, in cerebral hemispheres
- each connects with third ventricle via the interventricular foramen
- third ventricle surrounds the thalamus
- aquaduct leads through midbrain to the fourth ventricle, between MO and cerebellum
- merges with central canal
Cerebrospinal Fluid
- Produced mainly by small arteries and arterioles in the leptomeninges and choroid plexus
- Flows doen a pressure gradient from ventricles to subarachnoid space
- From subarachnoid space, enters venous system
CSF drainage
Drained from subarachnoid space via…
- venules of the subarachnoid space
- venous sinuses of the brain
- the lymphatic system vessels
CSF function
- gives brain buoyancy and support
- protects from mechanical trauma
- helps provide brain with nutrients
- serves as a medium for the diffusion of neuroendocrine and neurotransmitter substances
Cranial nerves
- Mammals, birds and reptiles have 12 pairs of cranial nerves
CN I-XII
CN I
Olfactory nerve; sensory
Distribution; nasal mucosa membrane
CN II
Optic nerve; sensory
Distribution; retina of the eye
CN III
Oculomotor nerve; motor
Distribution; most muscles of the eye and iris
CN IV
Trochlear nerve; motor
Effects; dorsal oblique muscles of the eye
CN V
Trigeminal nerve; mixed
Effects; SENSORY eye and face, MOTOR of mastication
CN VI
Abducens nerve; motor
Effects; retractor and lateral eye muscles
CN VII
Facial nerve; Mixed
SENSORY; region of ear and taste to 2/3 of tongue
MOTOR; muscles of facial expression
parasympathetic to mandibular and sublingual salivary glands
CN VIII
Vestibulocochlear nerve; sensory
- effects; cochlear (hearing) and semicircular canals (equilibrium)
CN IX
Glossopharyngeal nerve; Mixed
SENSORY; pharynx and taste to caudal third of tongue
MOTOR; muscles of pharynx
parasympathetic to parotid salivary glands
Blood pressure control; relaying chemoreceptor info from carotid artery
CN X
Vagus nerve; Mixed
SENSORY; to larynx and pharynx
MOTOR; muscles of larynx
parasympathetic to visceral structures of thorax and abdomen
CN XI
Accessory nerve; motor
motor muscles of shoulders and neck from spinal cord
CN XII
Hypoglossal nerve; motor
Motor muscles of tongue
Brain Vasculature
All species’ blood is pooled into the cerebral arterial circle before branching into the brain
- 5 pairs of arteries, 4 from the arterial circle
- Rostral, middle and caudal cerebral arteries and rostral cerebellar artery
- And caudal cerebellar artery, from basilar a.
PATTERN OF ARTERIAL BLOOD SUPPLY; dog, human and horse
- arterial circle is supplied from 3 sources
- internal carotid and basilar artery both supply the CAS and most other parts of the brain
- carotid blood reaches most of cerebral hemispheres apart from caudal region
- vertebral artery also supplies rest of the brain
PATTERN OF ARTERIAL BLOOD SUPPLY; cats and sheep
- the lumen of the proximal 2/3 of the internal carotid artery becomes occluded in the first few weeks of life
- Maxillary artery supplies CAS via rete mirabile, maxillary blood supplies all brain except caudal part of medulla oblongata
- Vertebral artery supplies medulla oblongata
PATTERN OF ARTERIAL BLOOD SUPPLY; ox
- like sheep and cats, proximal 2/3 of carotid a. is absent
- two anastomosing branches , one from maxillary a. the other from the vertebral a. both have rete mirabile
- CAS supplied by internal carotid, maxillary, occipital and vertebral arteries
