Download BIOL 4260 Human Evolu*onary Anatomy Lecture 11: Nervous

BIOL 4260 Human Evolu3onary Anatomy Lecture 11: Nervous System & Trunk Evolu3on Lecture 2: Fossil Record
L5 Lumbosacral trunk S1 Superior gluteal nerve Inferior gluteal nerve S2 SACRAL PLEXUS S3 S4 S5 SciaBc nerve Co1 Posterior femoral cutaneous nerve Pudendal nerve The sacral plexus, anterior view Subcostal nerve Iliohypogastric nerve Ilioinguinal nerve Genitofemoral nerve Lateral femoral cutaneous nerve Femoral nerve Superior gluteal nerve Inferior gluteal nerve Pudendal nerve Posterior femoral cutaneous nerve (cut) Obturator nerve SciaBc nerve Saphenous nerve Saphenous nerve Sural nerve Fibular nerve Common fibular nerve Tibial nerve Superficial fibular nerve Deep fibular nerve Sural nerve Saphenous nerve The lumbar and sacral plexuses, anterior view Tibial nerve Saphenous nerve Sural nerve Fibular nerve Superior gluteal nerve Inferior gluteal nerve Pudendal nerve Posterior femoral cutaneous nerve SciaBc nerve Saphenous nerve Sural nerve Fibular nerve Tibial nerve Common fibular nerve Medial sural cutaneous nerve Lateral sural cutaneous nerve Tibial nerve Sural nerve Saphenous nerve Sural nerve Saphenous nerve Tibial nerve Sural nerve Fibular nerve Medial plantar nerve Lateral plantar nerve The sacral plexus, posterior view Gluteus maximus (cut) Inferior gluteal nerve Pudendal nerve Perineal branch Hemorrhoidal branch Gluteus medius (cut) Gluteus minimus Superior gluteal nerve Piriformis Posterior femoral cutaneous nerve Perineal branches SciaBc nerve Descending cutaneous branch Semitendinosus A diagrammaBc posterior view of the right hip and lower limb detailing the distribuBon of peripheral nerves Biceps femoris (cut) Tibial nerve Popliteal artery and vein Medial sural cutaneous nerve Common fibular nerve Lateral sural cutaneous nerve Gastrocnemius Small saphenous vein Sural nerve Calcaneal tendon Tibial nerve (medial calcaneal branch) A diagrammaBc posterior view of the right hip and lower limb detailing the distribuBon of peripheral nerves Nerve Plexus
Summary of the spinal nerves
•  Cervical spinal nerves emerge from C1–C8 •  Thoracic spinal nerves emerge from T1–T12 •  Lumbar spinal nerves emerge from L1–L5 •  Sacral spinal nerves emerge from S1–S5 •  Coccygeal spinal nerves emerge from Co1 Occipital bone Spinal cord emerging from foramen magnum Cervical plexus (C1–C5) Cervical spinal nerves (C1–C8 ) Brachial plexus (C5–T1) Thoracic spinal nerves (T1–T12) Lumbar spinal nerves (L1–L5) Sacral plexus (L4–S4) Coccygeal nerves (Co1) Lumbar plexus (T12–L4) SciaBc nerve Sacral spinal nerves (S1–S5) emerging from sacral foramina Reflexes can be classified by development response complexity of circuit processing site Innate Reflexes SomaBc Reflexes MonosynapBc Spinal Reflexes • GeneBcally determined • Control skeletal muscle contracBons • Include superficial and stretch reflexes • One synapse • Processing in the spinal cord Acquired Reflexes Visceral (Autonomic) Reflexes PolysynapBc Cranial Reflexes • Learned • Control acBons of smooth and cardiac muscles, glands • MulBple synapses (two to several hundred) • Processing in the brain Dorsal root AcBvaBon of a sensory neuron Arrival of sBmulus and acBvaBon of receptor Receptor SensaBon relayed to the brain by collateral REFLEX ARC SBmulus Effector Response by effector Ventral root AcBvaBon of a motor neuron InformaBon processing in CNS KEY Sensory neuron (sBmulated) Excitatory interneuron Motor neuron (sBmulated) Sensory receptor Ganglion Sensory neuron CENTRAL NERVOUS SYSTEM CENTRAL NERVOUS SYSTEM Ganglion Sensory neuron Interneurons Circuit 2 Motor neuron Motor neurons Circuit 1 Sensory receptor (muscle spindle) Skeletal muscle 1 Skeletal muscle A monosynapBc reflex circuit involves a peripheral sensory neuron and a central motor neuron. In this example, sBmulaBon of the receptor will lead to a reflexive contracBon in a skeletal muscle. Skeletal muscle 2 A polysynapBc reflex circuit involves a sensory neuron, interneurons, and motor neurons. In this example, the sBmulaBon of the receptor leads to the coordinated contracBons of two different skeletal muscles. SBmulus. Stretching of muscle sBmulates muscle spindles AcBvaBon of a sensory neuron InformaBon processing at motor neuron Response. ContracBon of muscle Steps 1–5 are common to all stretch reflexes. AcBvaBon of motor neuron KEY Sensory neuron (sBmulated) Motor neuron (sBmulated) Receptor (muscle spindle) Spinal cord Stretch REFLEX ARC SBmulus Effector KEY ContracBon Response Sensory neuron (sBmulated) Motor neuron (sBmulated) The patellar reflex is controlled by muscle spindles in the quadriceps group. The sBmulus is a reflex hammer striking the muscle tendon, stretching the spindle fibers. This results in a sudden increase in the acBvity of the sensory neurons, which synapse on spinal motor neurons. The response occurs upon the acBvaBon of motor units in the quadriceps group, which produces an immediate increase in muscle tone and a reflexive kick. Sensory and Motor Tracts
Motor tracts
•  CNS transmits motor commands in response to sensory informa3on •  Motor commands are delivered by the: •  SomaBc nervous system (SNS): directs contrac3on of skeletal muscles •  Autonomic nervous system (ANS): directs the ac3vity of glands, smooth muscles, and cardiac muscle Upper motor neurons in primary motor cortex BRAIN SomaBc motor nuclei of brain stem Skeletal muscle Lower motor neurons SPINAL CORD SomaBc motor nuclei of spinal cord Skeletal muscle In the somaBc nervous system (SNS), an upper motor neuron in the CNS controls a lower-­‐motor neuron in the brain stem or spinal cord. The axon of the lower-­‐motor neuron has direct control over skeletal muscle fibers. SBmulaBon of the lower-­‐ motor neuron always has an excitatory effect on the skeletal muscle fibers. Visceral motor nuclei in hypothalamus BRAIN Preganglionic neuron Visceral Effectors Smooth muscle Glands Cardiac muscle Autonomic ganglia Ganglionic neurons Adipocytes Autonomic nuclei in brain stem SPINAL CORD Autonomic nuclei in spinal cord Preganglionic neuron In the autonomic nervous system (ANS), the axon of a preganglionic neuron in the CNS controls ganglionic neurons in the periphery. SBmulaBon of the ganglionic neurons may lead to excitaBon or inhibiBon of the visceral effector innervated. Levels of Somatic Motor Control
Summary of somatic motor control
•  Cerebral cortex ini3ates voluntary movement •  Informa3on goes to the basal nuclei and cerebellum •  These structures modify and coordinate the movements so they are performed in a smooth manner Motor associaBon areas Cerebral cortex Decision in frontal lobes Basal nuclei Cerebellum The planning stage: When a conscious decision is made to perform a specific movement, informaBon is relayed from the frontal lobes to motor associaBon areas. These areas in turn relay the informaBon to the cerebellum and basal nuclei. Cerebral cortex Motor associaBon areas Primary motor cortex Basal nuclei Cerebellum Other nuclei of the medial and lateral pathways CorBcospinal pathway Motor acBvity Lower motor neurons Movement: As the movement begins, the motor associaBon areas send instrucBons to the primary motor cortex. Feedback from the basal nuclei and cerebellum modifies those commands, and output along the conscious and subconscious pathways directs involuntary adjustments in posiBon and muscle tone. Lee cerebral hemisphere Gyri Sulci CEREBRUM • Conscious thought processes, intellectual funcBons • Memory storage and processing • Conscious and subconscious regulaBon of skeletal muscle contracBons Fissures DIENCEPHALON THALAMUS • Relay and processing centers for sensory informaBon HYPOTHALAMUS • Centers controlling emoBons, autonomic funcBons, and hormone producBon CEREBELLUM Spinal cord MESENCEPHALON Brain stem • Processing of visual and auditory data • GeneraBon of reflexive somaBc motor responses • Maintenance of consciousness PONS • Relays sensory informaBon to cerebellum and thalamus • Subconscious somaBc and visceral motor centers MEDULLA OBLONGATA • Relays sensory informaBon to thalamus and to other porBons of the brain stem • Autonomic centers for regulaBon of visceral funcBon (cardiovascular, respiratory, and digesBve system acBviBes) • Coordinates complex somaBc motor paderns • Adjusts output of other somaBc motor centers in brain and spinal cord An Introduction to the Organization of the Brain
Major Regions and Landmarks of the Brain
•  Medulla oblongata •  Pons •  Cerebellum •  Mesencephalon (midbrain) •  Diencephalon •  Cerebrum (telencephalon) An Introduction to the Organization of the Brain
Medulla oblongata
Relays informa3on to the thalamus and brain stem Regulates visceral func3on Pons
Relays informa3on to the thalamus and cerebellum Regulates subconscious soma3c and visceral motor centers Cerebellum
Coordinates soma3c motor func3on Adjusts output of soma3c motor centers resul3ng in smooth opera3on Mesencephalon (midbrain)
Processes visual and auditory data Maintains consciousness and alertness Diencephalon
Epithalamus Contains the pineal gland Thalamus Relays informa3on to the cerebrum Processes sensory informa3on Hypothalamus Involved in emo3ons, thirst, some habitual ac3vity Lee cerebral hemisphere Gyri Sulci CEREBRUM • Conscious thought processes, intellectual funcBons • Memory storage and processing • Conscious and subconscious regulaBon of skeletal muscle contracBons Fissures DIENCEPHALON THALAMUS • Relay and processing centers for sensory informaBon HYPOTHALAMUS • Centers controlling emoBons, autonomic funcBons, and hormone producBon CEREBELLUM Spinal cord MESENCEPHALON Brain stem • Processing of visual and auditory data • GeneraBon of reflexive somaBc motor responses • Maintenance of consciousness PONS • Relays sensory informaBon to cerebellum and thalamus • Subconscious somaBc and visceral motor centers MEDULLA OBLONGATA • Relays sensory informaBon to thalamus and to other porBons of the brain stem • Autonomic centers for regulaBon of visceral funcBon (cardiovascular, respiratory, and digesBve system acBviBes) • Coordinates complex somaBc motor paderns • Adjusts output of other somaBc motor centers in brain and spinal cord Gray and White Matter
Gray Matter and White Matter
Organization
Inner region of gray maUer Surrounded by tracts of white maUer Gray maUer consists of cell bodies Outline
•  Vertebrate adaptations
•  Vertebrae number
•  Rib cage shape
•  Bipedalism
Axial Skeletons of
Vertebrates
•  Chordates: flexible rod
•  Vertebrates: bony or cartilaginous vertebrae
-  Tetrapods: lateral flexion, expanded ribs to
strengthen body wall, sternum to anchor ribs
-  Mammals: A-P flexion, suspension
architecture
Lateral flexion
predominates
Vertebrate Power!
Loosely-linked elements provide mobility by
summing slight movements at each successive joint
Tetrapod Challenges
Origins of neck, sternum
Mammalian
revolution
Limbs under trunk,
some ribs eliminated,
spine is dorsally convex,
trunk suspended from spine:
“suspension bridge” or
“arched bow”
Mammalian Locomotion
New organization allows active flexion in a sagittal plane
Mammalian Spinal Columns
Cervical vertebrae
Almost all mammals have 7
vertebrae
“Cervical ribs” have become
transverse processes
Thoracic vertebrae
Primate Numbers
Cervical -Thoracic - Lumbar
• Human: 7 - 12 - 5
•  Chimpanzee: 7 - 13 - 4
•  Macaque: 7 - 12 - 7
•  Australopith: 7 - ? - 6
•  Early Homo: 7 - 12 - 6
Fossil Evidence
A. africanus - 6 lumbar
H. erectus - 6 lumbar
Human Vertebral Number Variation
•  Cervical - 7 (pretty invariant)
• Thoracic - 12 (11-13)
• Lumbar - 5 (4-6)
• Sacral - 5 (4-6)
“magic number” - 29
•  Caudal highly variable - 4 (2-5)
Functional Anatomy
Primate Rib Cages
Quadrupedal
monkey: deep AP
and laterally narrow
thorax
Suspensory hominoids:
relatively more narrow
AP, transversely wide
Rib Cage Shape
In coronal orientation
humans: barrel-shape
apes: funnel-shaped
Also note waist - zone of
separation
Ape Rib Cage
Anatomy
•  Funnel-shape adapted for climbing and suspension
•  Flared inferior aspect also accommodates more
abdominal viscera
Fossil Anatomy
•  Australopiths - smaller vertebral
bodies, large vertebral canals,larger
dorsal pillar, long processes
Different ways of being a biped
Also rib cage shape probably chimplike (funnel-shaped)
•  H. erectus - long spinous processes,
larger funnel-shaped rib cage
Bipedalism:A
Compromise
Lumbar lordosis
The Solution
lumbar wedging in females (dark bars)
Evolutionary Origin
Two A.
africanus
lumbar series
show lordosis
and
human-like
variation
Detailed inWhitcomb et al. 2007