Lecture 1 - CNS Development and Intro Flashcards
Central Nervous System
Brain and spinal cord
Brain
Sorts through and properly routes incoming sensory information; initiates, controls, and coordinates most muscular activity except simple reflexes; site of origin of 12 cranial nerve pairs (4 pairs carry parasympathetic fibers III, VII, IX, and X)
Functions of the Brain
Sensory, motor, and cognitive
Spinal Cord
First CNS structure encountered by most incoming sensory information except sensory fibers in cranial nerves; last relay station for most motor information except ANS motor fibers; site of coordination of most reflex arcs
PNS
Made up of transmission pathways carrying information between the CNS and external/internal environments; includes 12 pairs of cranial nerves, 31 pairs of spinal nerves, sensory receptors in the skin and wall of the gut tube as well as in tendons and skeletal muscles
ANS
Entirely motor; innervates smooth muscle and glands (viscera); subdivided into sympathetic (fight or flight; thoracolumbar) and parasympathetic systems (feed and breed; craniosacral)
Nucleus
Aggregation of dendrites and nerve cell bodies in the CNS
Ganglion
Aggregation of dendrites and nerve cell bodies in the PNS
Nerve
Bundle of fibers (axons) in the PNS
Tract
Bundle of fibers (axons) in the CNS
Commissure
Tract in the CNS that crosses from one side to the other
White Matter
Areas of myelinated axons
Gray Matter
Areas of unmyelinated axons, cell bodies, and dendrites
When does the formation of the nervous system occur during the embryonic stage?
End of 2nd week to end of 8th week
Stages in Neural Tube Development
Neural plate to neural folds to neural tube
Parts of Tripartite Brain
Prosencephalon (further divided in pentapartite brain), mesencephalon, and rhombencephalon (further divided in pentapartite brain)
Parts of Pentapartite Brain
Telencephalon (most anterior), diencephalon, mesencephalon, metencephalon, and myelencephalon
Anencephaly
Failure of the cranial end of the neural tube to close
Holoprosencephaly
Failure of prosencephalon to divide into 2 cerebral hemispheres; often associated with facial deformities such as a single orbit with 2 eyes, 1 eye, or no eyes, a proboscis-type nose located above the eye, or a cleft lip and palate
Spina Bifida Occulta
Results from a failure of the inferior neuropore to close; vertebral arch/es fail to develop in caudal area; spinal cord function is usually normal
Spina Bifida Cystica
Characterized by a sac-like cyst at the caudal end of spine; spinal cord and/or meninges may be found in the cyst; spinal cord function may be impaired; may be lower extremity dysfunction; bladder and bowel function may be impaired
Meningocele (form of spina bifida cystica)
Only meninges found in sac; spinal cord function may be impaired; signs and symptoms vary depending on location and severity of malformation
Meningomyelocele (form of spina bifida cystica)
Both meninges and spinal cord are found in sac; always results in abnormal growth of spinal cord; lower extremity paralysis; bowel and bladder dysfunction; loss of sensation to lower limbs
Myeloschisis (form of spina bifida cystica)
Failure of caudal neural folds to close; most severe of the defects
Arnold-Chiari Deformity
Inferior cerebellum and medulla are elongated and protrude into vertebral canal; medulla and pons are small and deformed; hydrocephalus; malformation of lower cranial nerves leads to deafness, tongue, facial muscle, lateral eye movement weakness
What is found in the lumina, floor, and roof of the telencephalon?
Lumina: Lateral ventricles 1 and 2
Floor: Basal nuclei (ganglia), olfactory lobes and nerves (subconscious motor control and muscle tone)
Roof: Cerebral cortex
What is found in the lumina, roof, walls, and floor of the diencephalon?
Lumen: Third ventricle
Roof: Epithalamus
Walls: Thalamus
Floor: Hypothalamus and infundibulum
Epithalamus
Habenular nuclei involved in emotional and visceral responses to odors; pineal body
Thalamus
Major relay center for afferent and efferent information to and from cerebrum and other areas of the brain
Hypothalamus
Mamillary bodies involved in olfactory reflexes and emotional responses to odors; supraoptic and paraventricular nuclei
Functions of Diencephalon
Controls and integrates ANS; associated with many kinds of visceral activity; intermediary between nervous and endocrine systems; controls normal body temperature; maintains extracellular fluid volume; biorhythm oscillator
What is found in the lumen, roof (tectum), and floor of mesencephalon?
Lumen: Cerebral aqueduct (of Sylvius)
Roof (Tectum): Superior colliculi (visual reflexes) and inferior colliculi (auditory and olfactory reflexes)
Floor: Tegmentum (red nucleus, substantia nigra, various tracts) and cranial nerve nuclei 3 and 4
What is found in the lumen, roof, and floor of metencephalon?
Lumen: Part of 4th ventricle
Roof: Cerebellum
Floor: Pons (cranial nerve nuclei 5-8; pontine nuclei, which is the relay between cerebrum and cerebellum; sleep center; respiratory center)
Cerebellum
Has a cortex and is connected to other parts of the brain via large pairs of fibers tracts called peduncles
Functions of Cerebellum
Coordinates skeletal muscle movements, maintain equilibrium and posture, and synergic control of muscle activity
What does the inferior peduncle connect to?
Connects to medulla and spinal cord
What does the middle peduncle connect to?
Pons
What does the superior peduncle connect to?
Midbrain
What is found in the lumen, main part, and roof of the myelencephalon?
Lumen: Rest of 4th ventricle
Main Part: Medulla obloganta
Roof: Posterior choroid plexus
Medulla Nuclei
Vestibular nuclear complex, sensory nuclei, and portions of reticular formation
Medulla Pyramids
Consist of lateral corticospinal tracts
Medulla Olives
Site of nuclei related to cerebellum
Medulla Reflex Centers
Cardiac center, vasomotor center, and centers related to respiration; various nonvital centers
White Ramus Communicans
Located in the thoracolumbar region prior to branching into dorsal/ventral primary ramus; carries myelinated PRE-ganglionic fibers
Gray Ramus Communicans
Located in the thoracolumbar region prior to branching into dorsal/ventral primary ramus; carries UN-myelinated POST-ganglionic fibers back to spinal nerve
What 2 major branches do spinal nerves divide into?
Dosal/Ventral primary rami
Paravertebral Ganglia
Linked together into a long chain on either side of the vertebral column in the thoracolumbar region; site of cell bodies of postganglionic sympathetic nerves; site of synapses between preganglionic myelinated sympathetic neurons and postganglionic non-myelinated sympathetic neurons
Splanchnic Nerve
Nerve supplying viscera
Prevertebral Ganglia
Typically found anterior to abdominal aorta; site of synapses between preganglionic myelinated sympathetic neurons and postganglionic non-myelinated neurons
Reflex Arc
Pathway that leaves from and returns to the CNS; consists minimally of a sensory pathway and a motor pathway
Afferent (Sensory) Pathways
Somatic afferent pathways carry sensation from non-visceral structures such as the skin and skeletal muscle; visceral (splanchnic) afferent pathways carry sensations from viscera
Efferent (Motor) Pathways
Somatic efferent pathways carry motor signals to skeletal muscles; visceral (splanchnic) motor pathways carry motor signals to smooth or cardiac muscles
Association Neurons (Interneurons)
Some reflex arcs consist only of an efferent neuron and an afferent neuron; most have intervening neurons (interneurons) in the CNS that modulate the interaction between the afferent and the efferent neurons
Monosynaptic Pathways
Pathways consisting only of afferent neurons and efferent neurons; each pathway has a single synapse
Polysynaptic Pathways
Pathways that include interneurons as well as afferent and efferent neurons; each pathway has multiple synapses
Resting Potential of Neuron Cell Body
-65mV
Excited Potential of Neuron Cell Body
-45mV; typically due to influx of Na+
Inhibited Potential of Neuron Cell Body
-70mV; typically due to influx of chloride ion or efflux of K+
Somatosensory Axis
Sequence of structures involved in the transmission of a sensory signal from the peripheral receptors to higher brain centers; components include:
Peripheral receptors, afferent neurons (primary, secondary, tertiary), spinal cord/brainstem, reticular substance (medulla, pons, mesencephalon), cerebellum, thalamus, and somesthetic areas of cerebral cortex
Primary Afferent Neurons
Synapse in the posterior horns of spinal cord or sensory nuclei in the brain
Secondary Afferent Neurons
Synapse in the thalamus
Tertiary Afferent Neurons
Synapse in the somesthetic areas of cerebral cortex
Skeletal Motor Nerve Axis
Sequence of structures involved in the transmission of an action potential from the higher brain centers to skeletal muscles; includes:
Motor cortex of cerebrum, efferent pathways (upper motor neurons extending from cortical areas to the anterior horns of the spinal cord and alpha/lower motor neurons extending to the skeletal muscles), and effectors (skeletal muscles)
Processing Areas of Skeletal Motor Nerve Axis include what structures?
Basal nuclei (putamen, globus pallidus, subthalamic nuclei) in the telencephalon, thalamus in the diencephalon, and spinal cord reflexes
