4 2 Dorsal and ventral rootlets of the lumbar and sacral spinal nerves are very long and continue down in the subarachnoid space all the way to the coccyx to find their appropriate intervertebral foramen to exit combination of lumbar and sacral rootlets is called cauda equina The Pia mater innermost layer of spinal meninges continues all the way down to the coccyx and the inferior end of this layer attaches to the coccyx and is called the filum terminale inferior anchoring filament of spinal cord Key words Pia Arachnoid Dura mater Conus medularis Cauda equina Filum terminale Denticulate ligament Ventral primary ramus Dorsal primary ramus Anterior median fissure Denticulate ligaments Shaped like the teeth on a saw Prevent spinal cord from moving Continuous with Arachnoid mater Slide 57 Figure 13 4 Dorsal primary rami supply erector spine Dura and Arachnoid mater end with the Dural sac around vertebra S2 Slide 60 shows that clinically if you know the anatomy of the spinal cord and you know where it ends at the upper lumbar level you can safely introduce a spinal needle into the subarachnoid space to inject anesthetics or take a sample of the cerebrospinal fluid to be analyzed Know where each region of the spinal cord ends i e dural sac begins continuously with foramen magnum and ends at S2 At the foramen magnum all three layers of the meninges of the spinal cord are continuous with with meninges surrounding the brain Herniated discs Figure 13 14 Will not be on exam Forms of synapses Divergence Spreads stimulation to multiple neurons or neuronal pools in the CNS Figure 13 16 Classification of reflexes Innate genetically determined vs Acquired learned Somatic control skeletal muscle contractions vs Visceral autonomic not conscious reflexes control actions of smooth and cardiac muscles glands and adipose tissue Monosynaptic one synapse vs Polysynaptic multiple synapses Spinal processing in the spinal cord vs Cranial processing in the brain 1 Sensory receptor responds to stimulus by producing a receptor potential 2 Sensory neuron conducts impulses via axon from receptor to integrating center 3 Integrating center within grey matter of spinal cord CNS relays impulses from sensory to motor neurons 4 Motor neuron receives signal from axon integrating center to effector 5 Effector muscle or gland responds to the motor nerve impulse All skeletal muscles contain receptors for stretch reflexes that are called muscle spindles Stretch reflexes are monosynaptic which means there is one synapse between the muscle and the nerve cell reflex occurs on the same side of the body spindle fibers send amount of stretch per muscle to the CNS Key words Intrafusal fiber spindle muscle spindle sensory nerve fibers Figure 13 15 Figure 13 14 Tendon reflex is a polysynaptic reflex because it involves more than one synapse between the incoming sensory fiber and the outgoing motor fibers Flexion withdrawal reflex Multi synaptic reflex Reflex occurs on the same side as the painful stimulus i e removing hand from hot surface when flexor muscles are stimulated to pull hand away the the extensor muscles are inhibited so that the hand may not go back to the hot surface Multi synaptic and multi segmental because it involves more than one segment of the spinal cord Crossed Extensor reflex Multi synaptic and multi segmental Figure 13 17 When one limb is off the ground the stimulus activates the other limb to become a rigid stabilizer Brain can modify this for daily activities such as walking and running Walking and running are modifications of flexion withdrawal and crossed extensor reflexes Cerebral Hemispheres Cerebrum and Cerebellum Cerebral cortex covers each of the two hemispheres Grey matter that covers the surface of each cerebral hemisphere is called the cerebral cortex Estimated that there is somewhere around 20x10 30 neurons per hemisphere Deep to cerebral cortex there is white matter which is composed of myelinated axons White matter has Association fibers Make connections within one hemisphere Association fibers can be categorized as Arcuate short connecting one gyrus to another or Longitudinal long connecting one lobe to another Commissural fibers Axons that cross the midline from one hemisphere to the other and help communication and sharing of information between the two hemispheres Projection fibers Connect cerebrum with lower areas Link the cortex with other structures such as brain stem and spinal cord Internal capsule is white matter composed of many projection fibers Deep longitudinal fissure separates the two hemispheres Called Superior Longitudinal Fissure Contains corpus callosum Cerebrum Conscious thought processes intellectual functions memory storage processing conscious and subconscious regulation of skeletal muscle contraction Cerebellum Each fold of connective tissue over the brain is called a gyrus Each groove that separate the gyri is called a sulcus Brain stem is composed of three parts 1 Dienchephalon 2 Midbrain 3 Pons The whole nervous system develops in the embryo from a hollow tube so by 6 weeks the brain has begun to develop rapidly Table 14 1 The brain is essentially a hollow tube in the early beginnings and portions of those hollow spaces become part of the ventricular system of the brain that is filled with cerebrospinal fluid Cerebral hemispheres left and right both have 4 defined lobes 1 Frontal lobe Motor and voluntary movement Anteriorly helps with planning future events and rational thoughts 2 Parietal lobe Processes information from the skin pain touch temperature pressure and the sense of movement in the joints and limbs 3 Occipital lobe Processes visual information from the eyes 4 Temporal lobe Processes auditory information and interpreting sounds and voices also helps with learning and memory On the lateral surface there is a sulcus that is almost vertical in orientation called the central sulcus and that is an important landmark for neurosurgery because it marks the anatomical separation between the frontal and parietal lobes Central sulcus is roughly placed at the location of the coronal suture Temporal lobe is partially separated from frontal parietal lobes by a deep lateral fissure Precentral gyrus is the location of the primary voluntary motor cortex Initiates voluntary movement Axons here go all the way down the spinal cord and command motor neurons in grey matter to cause contraction of the appropriate skeletal muscles for the appropriate pattern of movement